Advances in the interdisciplinary care of children with Klinefelter syndrome

Klinefelter syndrome (KS) is a common genetic disorder characterized by an additional X chromosome in males leading to a karyotype of 47,XXY. The clinical syndrome was first described nearly 75 years ago in several males with small testes, tall stature, gynecomastia, and azoospermia.¹ Our construct of what KS entails has greatly changed since then with identification of the genetic etiology in 1959, epidemiological studies of birth cohorts in the 1980’s, the development of rodent models, and many observational and interventional clinical studies in boys and men with KS.^2–4 Characterization of the neuropsychological profile, along with earlier diagnosis, facilitates earlier developmental evaluation and intervention services.⁵ Optimizing testosterone treatment may prevent some of the physical manifestations of the “classic KS phenotype.”⁶ Advanced Reproductive Technology (ART) has made it possible for nearly half of men with KS previously deemed infertile to have an opportunity to have a biological child.^7,8 Despite these scientific advances, the underlying molecular mechanisms underlying primary testicular failure and the phenotypic heterogeneity of physical and neurocognitive features observed in KS remains elusive. In this review, we will provide the pediatrician with an update on what is known about the clinical manifestations and current treatment recommendations for boys and men with KS.

Epidemiology and Diagnosis

KS is the most common sex chromosomal aneuploidy with estimated prevalence rates ranging between 1 in 448 to 1 in 917 male births.^9–14 A comparative analysis of newborn karyotyping studies published in the 1960–70’s and studies published in 1970’s–80’s reported an increase in the prevalence of KS.¹⁴ An increasing prevalence of KS could theoretically be explained by increasing maternal age, environmentally-derived increase of errors in paternal meiosis I, and decreasing rate of elective termination for prenatally diagnosed KS, although this increasing prevalence needs to be confirmed and further evaluated.^12,14,15 Epidemiological studies of sex chromosome aneuploidies have been limited to industrialized nationals, and to our knowledge, there have been no reports of ethnic differences in KS prevalence.

Currently, there is a significant discrepancy between the known prevalence of KS based on newborn screening studies and the rate of clinical diagnosis. It is estimated only 25–35% of males with KS are diagnosed in their lifetime, with the remaining 65–75% left undiagnosed. A study in the United Kingdom estimated that of all expected cases, ~10% of diagnoses are made in the prenatal period, 6% in childhood or adolescence, and 19% in adulthood.¹⁶ The small number of children who are diagnosed before puberty are typically identified due to underdeveloped genitalia, hypotonia, developmental delays, or learning and behavior problems. Diagnoses made in adolescence are secondary to small testicular size, gynecomastia, or rarely, incomplete puberty. Adults are most commonly diagnosed for infertility, however may present for symptoms of hypogonadism.¹³ The low rate of diagnosis in the pediatric population is due to a combination of factors, including subtle or underrecognized features that overlap with typical children and genetic testing practices of most pediatricians that do not cover the most common neurodevelopmental features in KS such as reading disabilities or speech-language disorders. Additionally, while the majority of boys with KS will have mild to moderate neurodevelopmental and/or learning difficulties, there is phenotypic heterogeneity and approximately a quarter of boys with KS do not exhibit these challenges.⁵ Finally, there appears to be a delay in diagnosis relative to when parents first expressed concern about their child to their physician, particularly for concerns of development.¹⁷ When initial parental concerns were due to developmental delays, there was on average 4.8 years before genetic testing confirmed KS. The delay in diagnosis was only 2 years when parental concern was pubertal development, microorchidism, or gynecomastia, however the average age of diagnosis in that cohort was still greater than 20 years of age.¹⁷ Therefore, recognition of features of KS by the pediatrician can result in increased diagnosis rate and more appropriate care.

The diagnosis of KS is made with pre- or postnatal karyotype or DNA microarray. Historically, prenatal screening by ultrasound and/or maternal serum biochemical markers dramatically increased identification of pregnancies at risk for autosomal aneuploidies, yet KS pregnancies have failed to correlate with these screening markers. However, new prenatal genetic screening technology, referred to as non-invasive prenatal testing (NIPT), analyzes cell-free fetal DNA circulating in maternal blood. This low-risk screening modality is typically performed in the first trimester and can detect sex chromosome aneuploidies (SCA). While sensitivity and specificity of NIPT is high for the detection of autosomal trisomies, there is a lower accuracy for sex chromosome aneuploidies. In a recent study by Meck et al, NIPT specific to XXY was shown to have a positive predictive value of only 67% (CI 22.3–95.7%).¹⁸ Moreover, a 2014 study by Wang et al identified that 8% NIPT+ for SCA were due to an abnormal maternal karyotype.¹⁹ Thus, in cases of NIPT+ for SCA, both follow-up diagnostic testing (by prenatal chorionic-villous sampling, amniocentesis, and/or postnatal blood testing) and maternal karyotyping are recommended. While a relatively high rate of false positives remain, NIPT creates a landmark opportunity to dramatically increase prenatal ascertainment of KS, with estimates citing the diagnosis rate for infants would increase tenfold if NIPT were to be standard screening for all pregnancies. There has also been discussion about including Fragile X on standard newborn screen, which would also identify some cases of KS.²⁰ With the possible increasing prevalence and significantly increasing childhood ascertainment rate, the pediatrician will likely care for more infants and children with a known diagnosis of KS.

Genetics

Klinefelter syndrome was confirmed to be attributed to the presence of a supernumerary X-chromosome resulting in a karyotype of 47,XXY by Dr. Patricia Jacobs in 1959.²¹ The supernumerary X-chromosome is acquired randomly predominantly through meiotic nondisjunction events during maternal or paternal gametogenesis or secondarily through post-zygotic nondisjunction during early embryonic mitotic divisions.²² The supernumerary X-chromosome is inherited from the mother in approximately 50% of cases, and from the father in the other 50%.²³ Up to half of cases with maternally-derived supernumerary X cases are due to errors in meiosis I and become more common with increasing maternal age, while maternal meiosis II nondisjunction errors and paternal errors are not associated with parental age. The 2008 Morris et al. study describing an increase in the prevalence of KS proposes that environmental factors have led to increased paternal meiosis I errors, however this finding remains controversial.¹⁴

Mosaicism

While approximately 90% of KS cases are non-mosaic 47,XXY, mosaicism is identified in approximately 7% of cases, and the other 3% are made up of rare variants.¹³ Mosaic forms of KS are identified when the XXY cell line is found in the presence of another cell line, such as 46,XY or other karyotypes (ie. 47,XYY or 47,XXX). The phenotypic variability of mosaic KS is dependent upon the karyotype and percentage of the additional cell lines. In cases of XXY/XY mosaicism, phenotypic symptoms may present more mildly and many cases fail to be identified. In cases of XXY mosaicism with abnormal karyotypes, such as XXY/XXYY or XXY/XXXY, phenotypic presentation may be more severe. Routine karyotype studies analyze ~20 cells, however in the case of possible mosaicism, additional testing should be pursued by florescence in situ hybridization (FISH) of the X and Y chromosomes to analyze a larger number of interphase nuclei. A significant limitation to testing for mosaicism is that peripheral blood may not accurately reflect levels of mosaicism across different tissue types, so phenotypic interpretation continues to be heavily dependent upon clinical evaluation.

Since the original 1959 report of KS being caused by a single extra X-chromosome, several other rare sex chromosome variations in males have been identified and characterized by the presence of two or more extra X and Y chromosomes, including 48,XXYY, 48,XXXY and 49,XXXXY syndromes, occurring in 1:18,000–1:100,000 male births. While these syndromes have been labeled as “variants” of KS because of shared features, including hypergonadotropic hypogonadism and tall stature, these syndromes are characterized by a more severe phenotype including additional physical findings, congenital malformations, medical problems and psychological features.^24,25

The mechanisms of how the presence of supernumerary X-chromosome(s) impact phenotypic features and variability observed in Klinefelter syndrome continue to be poorly understood. Studies continue to investigate the most implicated mechanisms including gene-dosage, skewed X-inactivation, genetic polymorphisms, and parental origin of the supernumerary X chromosome. Many of these potential mechanisms suggest an important role of epigenetic processes in KS.

Gene dosage and expression

Gene dosage compensation is the mechanism of equalizing gene expression between males (XY) and females (XX) due to the different number of genes contained on the sex chromosomes. This genetic equalization is achieved through a process of X-inactivation, in which one of the X-chromosomes in every female cell is randomly silenced, leaving only one X-chromosome transcriptionally active. In cases of X-chromosome aneuploidy, each X-chromosome in excess of one is inactivated by this same mechanism. However, two homologous regions of the sex chromosomes, known as pseudoautosomal regions (PAR1 & PAR2), as well as an additional 5–15% of X-chromosome genes escape inactivation and are expressed from both X-chromosomes.^26,27 An extra copy of these “escapee” genes are therefore transcriptionally active in males with KS, and overexpression then leads to excess mRNA and gene product, subsequently affecting the cellular and developmental pathways affected by these genes. The observation that clinical phenotype progressively deviates as the number of supernumerary sex chromosomes increase further supports this theory. This overexpression of escapee genes continues to be heavily studied as a likely mechanism leading to the phenotype and impacting phenotypic variability in KS.

An example of such an X-linked escapee gene is the short stature homeobox gene (SHOX), which has demonstrated a gene dosage impact in SCA’s. SHOX is located within the pseudoautosomal region (PAR1) of the X-chromosome and encodes a transcription factor expressed in the developing skeleton impacting height. Short stature seen in Turner syndrome (45,X) has been established to result from haploinsufficency of SHOX. While tall stature in Klinefelter syndrome partially results from slower closure of epiphyseal plates secondary to hypogonadism, SHOX overexpression has also been implicated in the accelerated growth velocity and increased height observed in sex chromosome trisomies. ²⁸

Further studies have analyzed differential genetic expression patterns in men with KS compared to male and female controls with the hope of elucidating differences in gene expression and regulation. In 2007, Vawter et al compared 11 men with KS to six XY males by whole genome expression array and identified differential expression of 129 genes, 14 of which were X-linked genes and many of which showed correlation with verbal cognition.²⁹ Additional studies evaluating genetic expression differences in brain, testes, and blood further suggest that autosomal genes are also differentially expressed in KS.^30–32 More recently, Zitzmann et al compared gene expression patterns of 132 males with KS to male and female controls. This study identified differential gene expression in 36 total genes (21 X-linked and 15 autosomal) compared to male controls and 86 total genes compared to female controls (46 Y-linked, 10 X-linked, and 30 autosomal).³³ Several of these identified X-linked genes are known to escape X-inactivation and are involved in pathways associated with phenotypic physical findings commonly seen in KS and therefore considered likely candidates to the pathophysiology of KS. Understanding the role of differential gene expression differences in KS is made more complex by the recent finding of increased copy number variations of X-chromosome genes in KS compared to typical males and females, most of which were duplications and falling within areas that escape X-inactivation.³⁴ Further work is needed to investigate regulatory mechanisms influencing differential gene expression not only in escapee genes but also across the entire genome as it relates to KS.

Skewed X-inactivation

Another genetic mechanism possibly leading to phenotypic variation in KS is skewed X-inactivation. Typically, X-inactivation is a random process resulting in a ratio of active to inactive X-chromosome alleles (outside of the PARs) of approximately 50%. Skewed X-inactivation, defined as greater than 80% methylation of one allele, results from preferential inactivation of a specific X-chromosome. Studies analyzing skewed X-inactivation in KS patients have ranged in finding below 10 percent to over 40 percent of subjects with skewing, and conflicting results regarding association of phenotypic features with skewing.^35–37

In 2014, Skakkebaek’s evaluation of 73 KS males found no association between skewed X inactivation and cognition or psychological phenotypic variation.³⁸ They did however find a significant correlation between skewed X inactivation and smaller grey matter volume in the left insula of the brain. The insular cortex area of the brain plays an important role in social, emotional and mental processing, all of which are variably affected in KS.³⁹ Caution should be taken for interpretation of results from any study of X-inactivation, however, as X-inactivation is typically measured in peripheral blood but can vary between tissues. Further, effects of skewed X-inactivation itself remain dependent on the polymorphisms and activity of the genes expressed from the more active chromosome, which varies between individuals.

Parental Origin

Several studies have analyzed phenotypic variability in KS based on parental origin of the supernumerary X chromosome and possible differential expression of maternal versus paternal alleles. To date these results have been inconsistent. While most studies are unable to establish a significant correlation between parental origin and phenotypic variability,^36,38,40,41 some studies have demonstrated a higher incidence of findings when the supernumerary X-chromosome was paternally derived, including developmental problems, altered steroidogenesis, increased hematocrit, later puberty, insulin resistance, and cardiac findings of a shorter QTc time.^33,42,43

Gene Polymorphisms

Another gene of interest in KS is the androgen receptor gene (AR), which is located on the X chromosome and contains a highly polymorphic CAG trinuclotide repeat, with a normal range of 9–37 CAG repeats.^36,44,45 Studies have correlated the CAG repeat length with physiological androgen effects, in which receptor activity is inversely related to the length of CAG repeat.³⁶ Several studies have demonstrated the CAG repeat length to be correlated with variable characteristics of the KS phenotype. Studies have reported a correlation of long CAG repeat length (low receptor activity) with height, arm span, likelihood for gynecomastia, small testes, HDL cholesterol, hematocrit, and later reactivation of pituitary-testicular axis, all of which are more characteristic of a more “severe” KS phenotype.^36,41,46 Additional studies have also demonstrated correlations of short CAG repeat length (high receptor activity) to longer penile length, higher bone density, and higher likelihood of having a stable partnership or professional employment.^36,43,47 Not all studies have supported phenotypic correlations with CAG repeat number, however, including a study of 73 men with KS where there was no correlation with psychological phenotypic variation,³⁸ and a study of 50 boys with KS where there was no relationship with cognitive or motor development.⁴⁸

Genetic Counseling

Genetic counseling in KS is important in multiple settings, including in the setting of a prenatal diagnosis, pediatric/adolescent cases with a new diagnosis, and in adulthood. For parents with an intrauterine diagnosis of KS, it is important for them to know there is no increased risk for miscarriage.⁴⁹ Prenatal or pediatric counseling should provide a comprehensive depiction of the phenotypic variability in KS, as well as include recommendations for developmental assessments/interventions, neuropsychological assessments/academic supports, social and emotional assessments/supports, indicated medical evaluations including endocrinology evaluation for testosterone replacement, current reproductive options, timing and approach to disclosure, and information regarding both local and national support groups.⁵⁰

Counseling regarding fertility and options for fathering children in KS has changed significantly in the past decade with advancing reproductive technology. Historically the presence of infertility in KS was considered universal, and azoospermia continues to be present in the vast majority of men with KS. However, research has supported that up to 8% of men with KS have a small number of sperm in ejaculate,^51,52 and there are rare case reports of spontaneous pregnancies. Much more promising is the current success rate of 50–60% in fathering biological children using advance reproductive techniques including microsurgical dissection of sperm from the testicle followed by in vitro fertilization, described in more detail in the endocrinology section below. While reported outcomes of children fathered from men with KS have been reassuring overall and most children have normal karyotypes, there have been slightly increased rates of children with KS and autosomal abnormalities reported. Pre-implantation genetic diagnosis is available.⁵³ Due to a relatively young field, these risks require additional research. Regardless, it is important that counseling in all cases of KS emphasize updated information about successes in the field of fertility, since this is a significant area of concern for parents, adolescents, and adults with KS.^54–56 It is also important to provide counseling related to other options for fatherhood chosen by many men with KS, including sperm donation and adoption.

Disclosure

With the advances in prenatal screening and increasing attention about KS in the medical literature, rates and ages of ascertainment are bound to improve. As such, pediatricians are often consulted by parents regarding decisions on when and how to disclose the diagnosis to the child. Research into other types of parent-to-child disclosures have identified barriers to communication causing possible avoidance of disclosure, including parents having difficulty understanding and/or being emotionally upset by the information, as well as being uncertain when and how to explain the information to the child and the child’s ability to understand.^57–59 A recent study by Dennis et al evaluated the disclosure process of an SCA diagnosis from both parents and individuals, including 68 parents of males with XXY and 58 individuals with XXY.⁶⁰ Study results identified important common themes and experiences, which led to formulation of recommendations supporting that the disclosure process include discussing the diagnosis gradually, honestly, and simply with age-appropriate terms and a positive attitude. Results further supported telling the child early, such as during childhood or before puberty, possibly prompted by when the child starts asking questions or if interventions are being pursued. Parents and individuals participating in this study encouraged the disclosure process to incorporate elements of support, including pointing out the child’s strengths, encouraging the child to ask questions, recognizing the common prevalence of the condition, and acknowledging research advancements and future possibilities.⁶¹ Resources for parents about disclosure are available at www.genetic.org.

Development, Behavior and Psychology

Early Development

There is significant variability in the developmental profiles of boys with KS, however there is an elevated risk for mild to moderate developmental delays for which monitoring is important so interventions can be implemented if needed. Prospective studies of infants with KS diagnosed by newborn screening identified speech-language delays in 75% and motor skills delays in 50%.^62–65 Average age of milestones including first words and first steps are each approximately 2–3 months later compared to typical XY peers. While these delays are milder in comparison to other genetic disorders such as Fragile X or Down syndrome, speech and motor deficits do not generally resolve without therapies and thus early intervention is recommended upon identification of a delay in one or more developmental domains. In 25–50% of cases, early development progresses typically without significant developmental concerns or apparent need for intervention.

In young boys with speech delays, language testing most often shows a pattern with receptive language skills higher than expressive skills.^62,66,67 An increased frequency of difficulties with oromotor planning and coordination called apraxia or dyspraxia of speech has also been described and can contribute to the expressive language delays in XXY.⁶⁸ Language difficulties can take a toll early in the development of self-expression and can impact tolerance for frustration, regulation of interpersonal challenges and are often sited as likely contributory factors to behavioral concerns.⁶⁹ Speech-language evaluation of the young child with KS should occur yearly for the first three years of life or upon diagnosis, and should include assessment of all language domains as well as evaluation for features of apraxia so that appropriate therapy techniques can be implemented.

Motor delays are present in about 50% of boys with KS, and hypotonia is commonly associated. ^48,70 Other common features such as mild hypermobility, pes planus with ankle pronation and/or genu valgum can further affect motor development. Motor domains including dexterity, coordination, and graphomotor skills are commonly areas of weakness, which can then lead to difficulties with handwriting and self-care skills such as dressing, tying shoes, and eating.^48,70,71 Physical and/or occupational therapy can be helpful for addressing motor and self-care difficulties. Orthotics are often prescribed for pes planus to support motor development and prevent lower extremity pain.

Cognitive, Language and Learning Profiles

Early studies of KS that reported increased rates of intellectual disability were flawed by ascertainment bias as they sampled populations from mental-health settings and long-term care facilities rather than a broader representative sample.^72–75 Since that time, our understanding of the cognitive profile in KS has evolved, and studies have established that the average full scale IQ ranges from 90–100, with expected variability around the mean from low to above average following a standard distribution. ^3,5,76 In this respect, many individuals with KS will not be significantly impacted by cognitive concerns and will achieve success in academic, personal, and career endeavors. On the other hand, statistically significant discrepancies have been shown relative to the general population and biological sibling controls. The overall mean for individuals with KS falls in the 90’s and 5 to 10 points lower than the population and sibling controls.^66,77–79 In most studies, Verbal IQ scores are found to be lower than Performance/Nonverbal IQ scores and it is these deficits in the verbal conceptual domain that account for the downward skewing of Full Scale IQ.⁷⁶ In this respect, nonverbal, visual perceptual, and spatial reasoning abilities are often an area of strength relative to verbal reasoning weaknesses.

Weaknesses in verbal skills align with speech-language profiles that commonly show difficulties in many language-related domains, and language disorders can be identified in 50–75% of boys with KS through adolescence.^66,67,80 Generally, basic receptive and expressive vocabulary skills are intact. As language skills advance and become more complex, higher-level language deficits are common, including poor grasp of verbal concepts, verbal processing difficulties, slow verbal processing speed, decreased verbal fluency, word retrieval problems, social communication difficulties, and difficulty with open-ended narrative construction.^{62,66,78,80–83} Understanding the behavior of males with KS in the context of their language abilities is important, both in terms of processing language and formulating verbal responses. For example, slower verbal processing can make highly verbal situations such as classroom lectures or interpersonal interactions more challenging or anxiety-provoking, and difficulty with word-retrieval and/or language formulation can then affect speed and content of verbal responses in both educational and social settings. Speech-language therapy can continue to play an important role beyond early language development, and speech-language evaluation is recommended for all children and teens with KS displaying behavioral, social, or educational difficulties to determine if therapies addressing higher-level language skills and social/pragmatic language may be helpful.

In the school-aged years, boys with KS are at higher risk than the general population for language-based learning disabilities, including dyslexia.^84,85 Occurrence ranges between 50 and 80%,^62,66,79 and family history of learning disability increases this risk.⁸⁶ More broadly, approximately 80% of boys with KS require some form of specialized support in school for language based learning or reading concerns.⁶² This is typically provided in the form of an Individualized Education Plan (IEP) or 504 plan, and it is strongly recommended that providers take an assertive stance with regard to advocating for intervention and educational supports. Lapses in support and intervention tend to create significant delays that are difficult to remediate. Evidence-based treatment approaches for reading disorders such as Linda-Mood-Bell or Orton-Gillingham are recommended, either through special education and/or private reading therapy. The high prevalence of learning disabilities in KS justifies periodic neuropsychological evaluation for all children with KS, starting in early grade school when early literacy is developing and deficits are simpler to address. Reassessment of cognitive and academic skills approximately every 3 years is then recommended, since deficits may not arise in some individuals until material becomes more complex and abstract with age. If lack of a formal learning disability diagnosis disqualifies a student from an IEP or educational supports, then advocating for services under the medical/health condition of KS with associated learning and executive functioning deficits is often successful to provide additional support.

Neuropsychological studies in KS have also consistently identified an increased risk for deficits in executive function (EF), including attention, working memory, cognitive flexibility, task initiation, fluency, and inhibition.^87–91 Executive dysfunction can have broad effects across home, school, and occupational settings, where additional supports in initiating, organizing, and executing tasks and assignments are often needed. Recent research in KS has also linked decreased EF and inhibition to increased behavioral difficulties including aggression, rule-breaking behavior, and thought problems.⁹² Neuropsychological and educational assessment in KS should include direct evaluation of EF, and parents and teachers should be educated about behavioral manifestations of EF difficulties, as well as effective interventions and supports, which should be included as part of a comprehensive educational plan.

There is an increased risk for attentional problems, and ADHD diagnosis rates range from 36% to 63%.^48,93,94 Distractibility and inattentive symptoms are more common than hyperactivity and impulsivity. It is important for children with KS who have attentional difficulties to have a neuropsychological evaluation that includes assessment of attention and EF, as well as other comorbidities that might present as inattention, such as learning disability, language disorder, or anxiety.^78,95,96 There is a positive response to treatment of ADHD symptoms with stimulant or nonstimulant ADHD medication in approximately 75% of patients, and thus a trial of medication(s) should be recommended as per standard ADHD treatment guidelines. However, as with other neurodevelopmental disorders, medications should be started at a lower dose and advanced conservatively while monitoring for side effects, and the contribution of comorbidities such as anxiety or learning disabilities should be considered if there is poor medication response or side effects. In complex or difficult cases, referral to developmental pediatrics or child psychiatry for medication management is recommended.

Behavior/Social-Emotional Development

Studies report a range of behavioral features and psychological risks that can be associated with KS, including behavioral difficulties, social-emotional immaturity, low frustration tolerance, decreased self-esteem, emotional sensitivity, along with higher rates of anxiety and depressive concerns.^{5,56,69,92,97–100} As with other associated features, there is broad variability in the presence and severity of these symptoms between individuals with KS. Behavioral and emotional concerns should be screened for routinely, with referrals made for further psychological evaluation and therapy/counseling as needed. Counselors and therapists often have to modify therapeutic approaches due to the presence of language disorders and difficulties with self-expression, and thus identifying a therapist with experience working with children with delays or disabilities is helpful. Occupational therapy approaches to teach sensory-based self-regulation strategies are often less verbal and can be very successful for patients with KS throughout childhood. Psychopharmacologic medication treatment should be considered in childhood through adulthood to address behavioral or emotional regulation, anxiety, or depression if these symptoms are affecting home, school, and/or social functioning.

Social difficulties and elevated rates of autism symptoms have also been described in KS.⁸³ Most studies have focused on describing autism symptoms which have identified features such as decreased social attention, decreased empathic skills, difficulty interpreting facial expressions, and social communication difficulties.^67,101–103 Studies that have included direct diagnostic assessment for autism spectrum disorders (ASD) are more limited, and report a rate of 27% in a Dutch cohort (n=51) using a standardized diagnostic autism interview called the ADI-R,⁹³ and a rate of 10% in an American cohort (n=20) using a battery including the ADI-R and direct assessment via the Autism Diagnostic Observation Scales (ADOS).⁵ Two other studies that evaluated rates of previous clinical ASD diagnosis in their cohort with KS also reported approximately 10% with ASD.^67,101 Recent important studies comparing autism symptoms and neuroanatomy in XXY to a group with idiopathic autism demonstrated that although behavioral questionnaires indicated similar autism symptoms between the groups, there were significant neuroanatomical differences in XXY compared to idiopathic ASD, suggesting that autism symptoms in the respective groups may have, at least partially, different etiologies.¹⁰³ Taken together, these studies support that ASD is an important clinical consideration in KS.

Screening for ASD should begin in early childhood as per the American Academy of Pediatrics recommendations, with referral for ASD assessment if indicated by screening results or if there are other concerns for ASD or social development raised by parents, teachers, or other providers. During assessment of social or ASD concerns, it is important and sometimes nuanced to differentiate the atypical social development and decreased reciprocity of ASD from social-emotional immaturity and/or expressive language deficits common in KS that can both also impact social relationships with peers. Further, it is common for concerns about ASD to become more apparent in boys with KS as social interactions become more complex beyond the first few years of life, and thus ASD evaluation should be included within a psychological evaluation for social or behavioral concerns. ASD diagnosis can be important in order to guide services and supports, as well as to help families, educators, and others better understand and support social development for the boy with KS.

Studies that drew subject-participation from clinical settings have reported elevated rates of a number of more complex psychiatric conditions, including bipolar disorder and psychotic spectrum disorders, with symptoms of paranoia, delusional thinking, and hallucinations.^93,102,104 Hospitalization for disorders associated with psychosis is reported as small in KS, but increased over the general population. ¹⁰⁵ Thus, providers should be aware of this increased risk and make referrals for psychiatric care if patients or parents bring up any concerns.

While we have emphasized many different cognitive, behavioral and social features that can be associated with KS, it is again important to emphasize the variability of the phenotype and the importance of also identifying areas of strengths and talent in each individual. While therapies and supports for areas of difficulty may be needed, it is equally important to encourage constructive opportunities for development in areas of strength and interest for positive self-esteem and quality of life. Parents should be encouraged to balance therapies and interventions with playtime, recreational or community activities, clubs/organizations that interest the child, and other positive activities.

Testicular Development and Function

One of the most commonly recognized features of KS is primary testicular insufficiency, which is present in the large majority of males with KS by early adulthood. The molecular mechanisms underlying this nearly universal manifestation remain elusive, however testicular development seems to be abnormal from very early in life.¹⁰⁶ The normal testis is made up of germ cells, Leydig cells, and Sertoli cells. From the limited studies reporting testicular biopsies in KS, germ cells are reduced in number from infancy and the deficit appears to be progressive, particularly after puberty, with only rare pockets of active spermatogonia seen in adulthood.¹⁰⁷ Evaluation of Leydig and Sertoli cell function largely relies on measurement of serum hormone concentrations. The Leydig cells produce testosterone, which has important local and systemic effects, and Sertoli cells produce inhibin B and anti-mullerian hormone (AMH), both of which have important local effects but unknown systemic effects. Assessment of serum hormone concentrations, particularly testosterone, is limited by assay variability, insensitivity of the assays in the hormone ranges typical of prepubertal children, and the observation that serum measurements do not necessarily accurately reflect intratesticular hormone concentrations. Regulation of gonadal function is primarily via the hypothalamic-pituitary-gonadal axis in which luteinizing hormone (LH) and follicle stimulating hormone (FSH) stimulate Leydig and Sertoli cells respectively. The hypothalamic-pituitary-gonadal axis is activated in the male during the first 2–3 months of life (often called the mini-puberty period of infancy), then again during puberty and remains active throughout the adult lifespan. There is overlap in testosterone levels in boys with and without KS, however males with KS on average seem to have lower serum testosterone (Figure 1).

Figure 1.

Graphical representation of testosterone concentrations throughout the lifespan in KS (solid) compared to typical 46,XY male (dashed).

Infancy

Hypogonadism in KS may start as early as fetal life or early infancy.¹⁰⁸ Evidence to support this includes a higher prevalence of underdeveloped genitalia and cryptorchidism in infants, reduced germ cell number in testicular biopsies, smaller testicular size, and several studies suggesting a blunted testosterone surge during the mini-puberty period of infancy.^109–112 Some endocrinologists measure testosterone, LH, and FSH around 6–12 weeks of life during the mini-puberty period of infancy. However, the mini-puberty period in the normal infant is vaguely defined, so it is not clear if this information has prognostic or management implications. Similarly, some providers will give testosterone during the first few months of life in infants with KS, however there is currently insufficient evidence to support this practice.¹¹³ Recent report of cognitive and behavioral benefits in males with KS who had previously received testosterone has stimulated a great deal of interest from families,^114,115 however these findings have to be replicated with prospective, randomized study designs. A randomized trial of intramuscular testosterone during the mini-puberty period of infancy is currently enrolling (NCT#02408445).

Endocrine evaluation during infancy should include measurement of stretched penile length and documentation of bilateral descended testes. If micropenis is present (<1.9 cm from 0–6 months of life) or the family desires further discussion regarding endocrinologic manifestations in infancy, referral to a pediatric endocrinologist should be sought.¹¹⁶ If cryptorchidism (persistent > 6 months), inguinal hernia, or any other urogenital malformations are present, the infant should be referred to Urology.

Childhood

Before puberty in boys with KS, testicular volume is often less than 2mL and penile growth throughout childhood has been noted to be slow.^40,117 The hypothalamic-pituitary-gonadal axis is quiescent in childhood, therefore, evaluation of LH, FSH and testosterone concentrations are generally not clinically useful. However, 10–20% of boys with KS may have prepubertal elevation of FSH, low inhibin B, and/or elevated AMH reflecting abnormal Sertoli cell function.¹¹⁸ Whether prepubertal Sertoli cell function is related to overall gonadal function in puberty and adulthood is yet to be determined. Results from a recently completed randomized controlled trial of oxandrolone (a non-aromatizable androgen) are expected soon. At this time, there are no recommendations for prepubertal hormonal evaluation or treatment.

Puberty

Most studies report a normal age of onset and tempo of early puberty in boys with KS.^3,119 Testes begin to enlarge but typically reach a peak volume of no more than 10 mL and then decrease down to < 4 mL.¹²⁰ Serum testosterone may rise appropriately in boys with KS in early puberty, but often eventually plateaus or even declines when serially monitored.¹²¹ FSH rises above the normal range on average a year after pubertal onset and LH approximately two years after pubertal onset. Endogenous testosterone usually supports virilization with penile enlargement and pubic hair development, although some young men with KS will not develop as much body or facial hair as would be expected for family. Fusion of the epiphyses may be delayed, contributing to tall stature. Gynecomastia probably occurs about as often as in pubertal boys without KS (~50%), however may be more likely to persist in KS.^122,123 Physical examination should always include palpation for breast tissue, and if present warrants consideration of testosterone supplementation. The pathophysiology of gynecomastia is an abnormal testosterone to estrogen ratio, therefore aromatase inhibitors have been used, however a randomized controlled trial in pubertal boys with physiologic gynecomastia (not KS) did not find benefit of anastrozole compared to placebo.¹²⁴ Estrogen receptor inhibitors (tamoxifen) have been reported in uncontrolled trials to reduce breast tissue size, however it is unclear if this is superior to the outcome without medication and no studies have been done in boys with KS.¹²⁵ Surgery can be considered if gynecomastia fails to resolve with time and hormone manipulation, however surgery does have perioperative risks and gynecomastia can recur postoperatively.¹²⁶

We recommend referral to an endocrinologist around 10 years of age or at the first sign of puberty, whichever is earliest. This initial visit is largely educational and establishes rapport. Boys with KS who have clinical signs of puberty should be monitored with pubertal examination and laboratory evaluation with serum LH, FSH, and testosterone approximately every 6 months. Currently there are no universally accepted guidelines for when (or if) to start androgen replacement. One option is waiting until clear biochemical and/or clinical evidence of hypogonadism with elevated LH, low or falling testosterone, and presence of gynecomastia, poor muscle mass, fatigue, or incomplete virilization. Another approach is to initiating low dose testosterone when LH has risen outside the normal range for pubertal development. A more aggressive option would be initiating testosterone in early puberty prior to any overt evidence of gonadal insufficiency. A randomized controlled trial that is currently enrolling hypothesizes psychosocial and motor benefits to low-dose testosterone treatment in early puberty (NCT#01585831). Until more evidence is available from research studies, the preference of the patient and parents should be greatly considered in determining the timing of androgen replacement.

Although there are many testosterone formulations available, options for adolescents are generally limited to depot injections of testosterone or topical testosterone gel, as other formulations do not allow for small enough dosing increments or are not well tolerated by adolescent boys.⁷ Injections have been used for decades and most endocrinologists are familiar with their use. Injections can be given at home or in the primary care physician’s office and dosing is typically titrated based on symptomatology and psychical examination. Disadvantages of injections include the presence of peaks and troughs in serum testosterone and the inconvenience and/or pain of shots. Topical testosterone gels are newer and may not be covered by all insurance carriers. If starting with gel, the smallest increment of the lowest potency available is recommended as the starting dose, with the goal of achieving serum testosterone conentrations in the normal range for pubertal stage. Disadvantages of gels include the need for daily application, skin irritation or sensory issues. Occasionally even the lowest available gel doses are too high for some pubertal boys, which may lead to elevated testosterone concentrations and subsequent rapid pubertal progression and/or premature fusion of the growth plates. Long-acting injections or testosterone pellets are being increasingly used in the US, however these are not recommended until late adolescence or adulthood when steady dose needs have been established.

Adulthood

The focus of this review precludes a comprehensive discussion on testicular function in adult men with KS. In brief, testicular size is universally small and usually firm as the germ cells that should make up the bulk of the testis volume in adults are profoundly reduced in KS.¹²³ It is important to note, however, that the male genitalia otherwise has normal structure, size and function. Nearly all untreated men with non-mosaic KS will have elevated LH and FSH, with low or low-normal testosterone and low or undetectable inhibin B and AMH.⁷ Testosterone replacement should be offered to all men with evidence of hypergonadotropic hypogonadism even if they are asymptomatic, as many manifestations of gonadal insufficiency may be subtle. The Endocrine Society has published guidelines for testosterone replacement in men with hypogonadism.¹²⁷

Azoospermia is nearly universal, however the concept of “universal infertility” in KS has drastically changed with the advanced reproductive technology technique of testicular sperm extraction (TESE) followed by intracytoplasmic sperm injection (ICSI).⁸ Using these techniques, small pockets of testicular tissue producing a few sperm can be identified during microsurgery, which are then extracted and injected through ICSI into a retrieved ovum, followed by in vitro fertilization. Currently, success rates of 50–75% are reported in adult men with KS seeking biological paternity using TESE and ICSI.^128,129 Studies have not found consistent predictors for which individuals will be more likely to have success with TESE, although mosaicism with a 46,XY cell line may have a more favorable outcome and older age (particularly more than 30 years), has been reported to have a less favorable outcome.^130,131 Many centers internationally have explored TESE for sperm cryopreservation from adolescents with KS, and current success rates do not consistently exceed those achieved in adulthood.^128,132 Based on this evidence and the relative newness of the field, we recommend that families are informed of the active and promising research in this field, and that consultation with a reproductive urologist is offered for all interested families, adolescents, or adults with KS seeking more information and options related to fertility. Invasive procedures for fertility preservation in childhood or adolescents are not currently routine practice outside of research protocols, although this may change as technology advances. Also important, several studies report similar fertility potential for males with KS with previous exogenous testosterone exposure,^128,129,131 therefore testosterone treatment should not be withheld from hypogonadal males for future fertility concerns.

Other Medical Issues

Insulin Resistance and Cardiovascular Disorders

Adults with KS are known to have a high prevalence of disorders related to insulin resistance including type 2 diabetes mellitus, dyslipidemia, and fatty liver disease.¹³³ Metabolic syndrome, a constellation of signs including large waist circumference, dyslipidemia, elevated fasting blood glucose, and high blood pressure, is present in around 50% of men with KS.^134–136 The presence of these conditions correlate with abnormal body composition (particularly abdominal adiposity) and hypogonadism. ¹³⁶ Together, type 2 diabetes and cardiovascular diseases yield a standardized mortality ratio of 5.8 in adults with KS.¹³⁷

Much less work has been done in children with KS, however recent studies have found a high prevalence of metabolic syndrome features as well as a high body fat percentage in this population.^138,139 Importantly, features of metabolic syndrome in boys with KS appear to be independent of age or BMI. Counseling regarding a healthy diet and regular exercise is imperative from an early age. We recommend cholesterol screening with a fasting lipid panel in at age 9–11 years and after puberty is completed (consistent with American Academy of Pediatrics recommendations for all children), and sooner if additional risk factors are present.¹⁴⁰ Lipid panel should be repeated in puberty if the previous panel was abnormal or additional risk factors are present such as obesity, untreated hypogonadism, or atypical antipsychotic use.

The risk of peripheral vascular disease and thromboembolic disease is increased in males with KS, resulting in significantly increased mortality.¹³⁷ Venous stasis and recurrent leg ulcers are also quite common.^141,142 Although these conditions are more common with age, we have had several adolescents with KS who developed venous thrombus in at-risk situations such as with a central venous catheter or surgery with immobilization. Consideration of prophylaxis measures should be considered if an adolescent or young adult is in a clinical situation that may predispose to clotting.

Bone Health

Studies in adult men with KS report lower bone mineral density and a higher morbidity and mortality from hip and spine fractures.^137,143 It is speculated hypogonadism contributes to these findings, however a mouse model suggests the additional X chromosome itself results in abnormal bone structure.¹⁴⁴ A single study in 18 children and adolescents with KS reports normal bone mineral density. ¹³⁸ In our anecdotal experience, we have not seen a high prevalence of pathologic fractures in children and adolescents with KS, and we do not recommend routine evaluation of bone mineral density. We do recommend attention to standard pediatric guidelines and ensuring adequate calcium and vitamin D intake, regular physical exercise, maintaining a normal BMI, and tobacco avoidance.¹⁴⁵ For post-pubertal boys with KS, maintenance of sex steroid levels in the normal range likely helps bone density.¹⁴⁶ Chronic or unexplained back pain in an adolescent or adult with KS should raise concern for a vertebral compression fracture and appropriate evaluation undertaken.

Autoimmunity

Many case series and later epidemiological studies have reported an increased prevalence of several autoimmune diseases in KS compared to 46,XY males. A recent medical record linkage study of hospitalized men in England found significantly higher rates of several autoimmune diseases in men with KS including rheumatoid arthritis (RR 3.3), lupus, multiple sclerosis (RR18.1), Addison’s disease (RR 11.7), Sjogren’s syndrome (RR 19.3), autoimmune hypothyroidism (RR 2.7), and type 1 diabetes mellitus (RR 6.1).¹⁴⁷ Although these are all significantly higher in adult men with KS compared to men in the general population, most of these autoimmune conditions are known to have a female predominance, and the risk of these autoimmune diseases is similar to women in the general population.¹⁴⁸ No studies have evaluated autoimmune diseases in children with KS. Although screening for primary hypothyroidism is often recommended in KS,¹⁴⁹ evidence is lacking to recommend this in pediatrics. It is important to be aware of the increased prevalence of autoimmunity in KS and evaluate if suggestive symptoms are present.

Malignancy

An excellent review of the literature of malignancies in KS was published in 2013.¹⁵⁰ Despite abundant case reports, there are few epidemiological studies available. Because only a minority of males with KS are diagnosed before adulthood, the natural history of malignancies in children with KS is really not known. The three cancers that are consistently found to be more prevalent in KS compared to males in the general population are breast cancer, extragonadal germ cell tumors, and non-Hodgkin’s lymphoma. No routine screenings are recommended for any of these malignancies in childhood, but suspicious symptoms should be evaluated.

Breast cancer is around 20 times more common in men with KS compared to men without KS, however it is still less common than in women.¹⁵¹ Overall, breast cancer affects ~3–7% of men with KS,^152,153 but is very rare in adolescents. Self exams as well as regular physician exams should be routine, and any palpable mass should be evaluated.

Extragonadal germ cell tumors are diagnosed in ~0.1% of males with KS, representing a large increased risk compared to the general population. Unlike breast cancer which does not typically present until adulthood, around half the reported cases of extragonadal germ cell tumors occur in pediatrics with a peak age in adolescence.¹⁵⁴ Precocious puberty is the most common presenting symptom in boys <10 years of age, while cough, dyspnea or chest pain was most common in adolescents and adults given the most common tumor location is the mediastinum.¹⁵⁵ If these symptoms are present, extragonadal germ cell tumor should be suspected evaluation pursued with a chest x-ray to evaluate for a mediastinal mass as well as measurement of serum β-HCG and alpha-fetoprotein.¹⁵⁰

Finally, an association with non-Hodgkin’s lymphoma was reported in a large British cohort, particularly in boys with more than three sex chromosomes (48,XXYY), however this was not found in other studies and requires further investigation.¹⁵¹ There are many case reports of other hematological malignancies in males with KS, however epidemiological studies do not show an increased incidence or mortality from leukemias or other lymphomas in KS.¹⁵⁶ It is important to keep in mind, however, that leukemia is most common cancer in childhood and therefore it would still be more likely for a boy with KS to develop leukemia than any of the other malignancies described above.

Other Medical Conditions

Congenital anomalies are more prevalent in infants with KS than in the general population and lead to a higher mortality.¹³⁷ Congenital anomalies are much more common in boys with more than three sex chromosomes.¹⁵⁷ The most frequently reported anomalies include inguinal hernia, congenital heart disease, cleft palate and velopharyngeal insufficiency, and kidney malformations. Dental conditions, particularly taurodontism and frequent caries possibly from enamel defects, are very common,^24,158 and children with KS should have regular dental care.

Multiple case series have reported seizures in boys with KS, and a large epidemiological study from Britain found a standardized mortality ratio from epilepsy of 7.2 in males with KS compared to the general population.¹³⁷ Seizures are present in 15% of males with 48,XXYY syndrome.²⁴ Seizures can present at any age. Tremor is also noted, particularly in males with more than three sex chromosomes starting in adolescence.^24,159

Little is reported in the literature on atopy in KS, however we appreciate a high prevalence of asthma and allergies in children with KS. In a study of 95 males with 48XXYY syndrome, 55 and 60% had allergies and asthma respectively.²⁴ Death from chronic lower respiratory disease, which would include asthma, was twice as likely in men with KS compared to the general population in Britain. ¹³⁷ Further investigation is needed to explore whether this is a true association.

In summary, KS is a common but under-diagnosed genetic condition with significant phenotypic variability in childhood. The pediatrician needs to be aware of the increased risk for neurodevelopmental, psychological, and medical conditions that are associated with an additional X chromosome. Over the next decade we anticipate a sharp increase in diagnoses rates with advances in genetics, particularly prenatal and neonatal diagnoses. In the US, more multidisciplinary clinics are being established to provide comprehensive care for children and adults with KS and other sex chromosome variations.⁹⁶ More research is needed to further define the natural history of KS in infancy and childhood with these unbiased populations, as well as understand genetic and environmental contributors to phenotypic variability and determine best practice screening and management guidelines for boys with KS.

TABLE 1.

Pediatric Evaluation and Treatment Recommendations for XXY/Klinefelter syndrome

Neurodevelopmental/Psychological Risk	Recommendation for Follow-Up and Further Evaluation
Developmental delay (Age 0–3)	Developmental and ASD Screening by PCP per AAP recommendations, and Referral for comprehensive developmental assessments for all children, with evaluation of cognitive, speech-language, motor, social, and adaptive functioning domains using standardized measures. If prenatal diagnosis: Evaluations at 9–15 months, 18–24 months, and 30–36 months. Sooner or more frequent if any developmental concerns. If postnatal diagnosis: Evaluation at diagnosis, and then at ages recommended above. If indicated, initiation of early interventions including developmental, speech, occupational, physical, or behavioral therapies.
Learning Disabilities	Monitoring of learning and academic performance from preschool throughout education. Psychological evaluations to assess cognitive functioning, learning disabilities (reading and/or math) at key times during education and transitions: early elementary, late elementary, middle school, high school, transition to post-secondary programming/education. Special education supports (504 plans or Individual Education Plans) as needed. Evidence-based interventions for learning disabilities if identified. Consideration of additional academic supports, tutoring, options for schools/educational settings
ADHD/Executive functioning (EF) problems	Education of parents/caretakers about EF and manifestations of symptoms of EF deficits. Screening by school system and PCP with input from family and school as presentation may vary in different environments. Recognition that ADHD-Inattentive symptoms are more common in XXY. Formal evaluation of executive functioning and attention by psychologist or neuropsychologist beginning at 7–8 years of age, and at key times during education: late elementary, middle school, high school, transition to post-secondary programming. Implementation of educational strategies and supports for EF and ADHD symptoms at school and home if present. Consideration of medication treatment for attention disorders/ADHD if present.
Speech-Language disorders	Assessment with an experienced pediatric speech and language pathologist with evaluation of expressive-receptive language abilities, higher-order language skills, pragmatic/social use of language, and disorders of speech production (developmental dyspraxia/apraxia) or hypernasality due to possible velopharyngeal insufficiency (VPI). Recommended yearly from birth to 4 years, then every 2–3 years depending on presence or severity of impairment. Referral to ENT if concerns of hypernasality, VPI Speech-language therapy through early intervention, school system and/or privately if indicated. Consideration of role of speech difficulties in behavior/frustration.
Motor skills	Beyond age 3, monitoring of fine and gross motor skills, balance, coordination, motor planning. Occupational and/or physical therapy interventions if motor deficits causing difficulties with handwriting, play or recreational activities, dressing, eating or other self-care skills.
Social skills difficulties	Social Development and ASD Screening by PCP per AAP recommendations, and Evaluation by developmental pediatrician, child psychiatrist and/or psychologist for evaluation if concerns of social functioning or ASD Consideration of whether social immaturity and/or language deficits contribute to social difficulties Therapy/counseling, school supports and/or medication treatment if indicated. Consideration of social skills therapy/groups in academic setting or privately Involvement in clubs/activities of interest where peers share interests If ASD, evidence-based and individualized Applied Behavior Analysis (ABA) therapies such as ESDM
Emotional/Behavioral Difficulties, Anxiety	Evaluation by developmental pediatrician, child psychiatrist and/or psychologist for evaluation and treatment if concerns. Involvement of school psychology/counseling team, incorporation of behavioral supports in school environment, consideration of contributions of bullying Consideration of behavioral responses relative to developmental level Adaptations should be made in therapy approach if language deficits are present, parental involvement in therapy Consideration of medication treatment as indicated for anxiety, emotional lability, depression, mood dysregulation, irritability Consideration of OT/Sensory-based approaches to address self-regulation, especially in younger ages or for if difficulties with self-expression during therapy Consideration of complementary therapies including equine therapy, art/music therapy, yoga, etc.
Adaptive functioning problems	Evaluation of adaptive functioning using standardized measures including domains of self-care, communication, social, community use, safety and self-direction should be included as part of the psychological or educational evaluations recommended above. Consideration of OT or other therapies for support throughout childhood and adolescence
Medical Features/Risks	Recommendation for Follow-Up and Further Evaluation
Cardiovascular
Congenital anomalies	Cardiology consultation and/or Echocardiogram/EKG for all new diagnoses or after birth in a prenatal diagnosis.
Dyslipidemia	Cholesterol screening with lipid panel at age 9–11 and then again after puberty per AAP. Sooner and/or more frequent if family history and/or noted abnormalities.
Abdominal obesity, fatty liver disease, insulin resistance, Metabolic syndrome	Anticipatory guidance for establishing a healthy diet and active lifestyle in childhood. If obesity is present, screening should include ALT and HbA1C. Referral to weight management programs if indicated.
Dental
Enamel defects/caries Taurodauntism	Dental evaluation beginning at age 1, followed by dental visits twice per year or per dentist recommendation.
Endocrinologic
Hypogonadism/Testosterone deficiency	Consider consultation with Pediatric Endocrinology around 2 months of age. Pubertal examination with every annual physical exam. Referral to Pediatric Endocrinology at first sign of puberty or by age 10 years. Monitoring of serum gonadotropins and testosterone every 6 months when pubertal. Consideration of testosterone supplementation based on provider assessment and family preference. The goal of treatment is to replace deficient endogenous testosterone production and support development of secondary sex characteristics, bone health, metabolic function, psychosocial health, and prevent consequences of hypogonadism including gynecomastia and tall stature. Over treatment should be avoided.
Gynecomastia	Palpation for breast tissue with every annual physical exam. Early referral to Endocrinology for any gynecomastia. Consideration of treatment with testosterone, aromatase inhibitors, and anti-estrogens, and/or surgical resection if medical management fails.
Subfertility	Consider semen analysis in adolescence if developmentally appropriate. Consider referral to Reproductive Urologist with experience in TESE in KS if desired.
Osteopenia/Osteoporosis	Ensure adequate dietary intake of calcium and vitamin D. Consider measurement of vitamin D stores and replacement if deficient. No role for routine bone density measurement in pediatrics.
Genetics	If a prenatal diagnosis, postnatal confirmatory genetic testing is recommended, including FISH testing for mosaicism. Consultation with genetic counselor and/or clinical genetics upon diagnosis. Consultation in early adulthood; consider preimplantation genetic testing if paternity is pursued.
Genitourinary
Undescended testes, inguinal hernia, hypospadias	Referral to Urology if present. Consider testicular tissue biopsy and preservation if surgery is indicated.
Microphallus	Referral to Pediatric endocrinology or Urology if present in infancy. Short course of testosterone can be discussed.
GI/Feeding
Newborn feeding difficulties	Lactation specialist, feeding therapy through occupational (OT) or speech therapist if indicated. Weight/growth monitoring by PCP.
Reflux/Constipation/Abdominal complaints	Evaluation and treatment with primary care provider if present. Referral to GI if indicated. Consideration of Eosinophilic esophagitis.
Hematology/Oncology
Hypercoaguability	Awareness of increased hypercoagulable risk and symptoms (DVT, PE). Prophylaxis in high-risk clinical situations (orthopedic surgery, central lines, etc) Hypercoaguability evaluation and/or referral to Hematology if blood clot diagnosed
Malignancy risk	Palpation for breast tissue with every annual physical exam. Evaluation of any discrete masses. CXR to rule out mediastinal mass if symptoms of cough, dyspnea, or chest pain. Immediate evaluation/endocrine referral for precocious puberty. Eval to include serum β-HCG and alpha-fetoprotein.
Immunology
Autoimmune diseases	Discussion and monitoring of symptoms autoimmune disease with PCP. Thyroid function screening every 1–2 years starting at age 10, sooner or more frequent if symptoms of hypo or hyperthyroidism are present.
Musculoskeletal
Pes Planus (Flat feet)/Ankle pronation	Referral to PT or orthopedics for consideration of orthotics if causing pain, limiting activities, or affecting motor coordination or motor skills.
Tall stature	Considerations of adaptations if needed at home and school (i.e. larger chairs/desks) Recognition that tall stature can lead to expectations of more mature behavioral functioning, when social maturity in KS may be average or slightly delayed relative to peers
Neurologic
Seizures	Neurologic history, including questions about staring spells or atypical movements. Neurology consultation and/or EEG and brain MRI may be indicated. Anticonvulsant medication(s) if indicated.
Tremor	Monitoring for intention and/or postural tremor, most commonly in upper extremities Referral to Neurology and consideration of medication as needed or for daily use if interfering with school (handwriting), work tasks, daily living skills (dressing, eating)
Pulmonary
Allergies/Reactive Airways/Respiratory Infections	Management through PCP, referral if needed.
Sleep Apnea	Sleep study if symptoms of sleep apnea present (i.e. daytime fatigue, short sleep latency, difficulty with morning awakening, snoring, apnea)