A Novel FGFR1 Mutation Causing Familial Normosmic Hypogonadotropic Hypogonadism in Three Sisters

Introduction

Idiopathic hypogonadotropic hypogonadism (IHH) is a genetic disorder characterized by defective GnRH secretion resulting in low sex steroid concentration, and low levels of gonadotropins causing absent or delayed puberty. IHH when associated with a defective sense of smell, anosmia, or hyposmia then is termed Kallman syndrome and patients with normal sense of smell are referred to as normosmic IHH (nIHH). The incidence of the nIHH is 1–10 in 100,000 live birth and 50–60% of IHH patients have defective sense of smell (Kallman Syndrome) [1]. We are reporting the case of IHH with non-reproductive symptoms in three sisters which is mainly associated with gonadotropin deficiency. IHH can be inherited as autosmal dominant, autosomal recessive, or X-linked pattern representing clinical and genetical heterogenisity with > 25% different genes responsible for the IHH till date. In contingent with gene mutations, cleft lip or palate, renal agenesis, dental agenesis, ear anomalies, congenital hearing impairment, bimanual synkinesis, or skeletal anomalies are associated with IHH. This warrants the multidisciplinary approach for these patients to address their clinical symptoms according to system involved at different age groups.

Case Report

An 18 years old girl presented with chief complaint of primary amenorrhea along with absent breast & pubic hair development. She never had cyclical abdominal pain and spotting before. She didn't have any eating disorder, nor was involved in any athletic activities. She never had any chronic illness and prolonged drug intake. Her parents had non-consanguineous marriage and her two younger sisters aged 16 and 12 years had, similar complaints of absent puberty. Her mother attained premature menopause at age of 38 years. Patient had done ultrasound one year back which showed a very small sized uterus 2 cm × 1.8 cm x 1.2 cm with non-visualization of endometrium and was mislabeled as MRKH Syndrome. However, absence thelarche is not a feature of the MRKH syndrome and was not evaluated further. Table 1 elaborates the clinical findings and investigations of all three sisters, showing similar findings in all three.

Table 1.

Clinical features of 3 sisters

	Sister1	Sister 2	Sister 3
Height	160	158	159
Weight	45.5 kg	46.2 kg	44.8 kg
BMI	17.7 kg/m2
GPE	Absent lateral incisors and increased gap between central incisors Hallux Valgus
IQ	Normal	Normal	Normal
Breast	Tanner Stage1	Tanner stage 1	Tanner Stage 1
Pubic	Tanner Stage1	Tanner Stage1	Tanner Stage1
Axillary	Absent	Absent	Absent
External genital	Normal	Normal	Normal
Vagina	8 cm	9 cm	8 cm
Uterus	Hypoplastic uterus 2 cm*2 cm*1 cm	Hypoplastic uterus 1.8 cm*2 cm*1.6 cm	Hypoplastic uterus 1.8 cm*1.8 cm*1.5 cm
FSH in mIU/μL (3.5–12.5mIU/L)	2.32	1.9	2.0
LH in mIU/ul (1.68–15 IU/L)	1.8	1.7	1.5
E2 in pg/ml (21–251 pg/ml))	20.35	17.9	16.81
Cortisol in mcg/dL (5–25 mcg/dl)	5.02	5.11	4.98
TSH in μIU (0.27–4.20μMIU/ml)	1.99	2.01	1.6
Prolactin in ng/ml (4.75–23.3 ng/ml)	15.6	18.2	16.8

She had clinical hypoestrogenism for which a hormonal profile was done (described in Table 1) leading to diagnosis of hypogonadotropic hypogonadism. A blindfolded test for smell was done using different odorants like spirit and deodorant, however a formal olfactory test was not done. Her skeletal survey showed delayed bone age by 2 years and features of osteopenia. MRI of hypothalamus pituitary axis showed normal olfactory bulbs. Since there was isolated deficiency of gonadotropins without anosmia, a final diagnosis of idiopathic congenital normosmic hypogonadotropic hypogonadism was made.

Both the elder sisters were started on HRT with 1 mg estradiol valerate continuously for 4 months for breast development. Breast tissue grew from Tanner stage II to III. This was followed by cyclical hormonal therapy. Cyclical hormonal therapy with 1 mg oral Estradiol valerate for 28 days with addition of oral Progesterone in last 5 days. She has withdrawal bleeding after 1 month which lasted for 3 days. Her uterus also grew from 2 cm × 1.8 cm × 1.2 cm to 5.1 cm × 4.2 cm × 3 cm. She was put on cyclical Estrogen and Progesterone therapy and had menses every month. Her younger sisters also achieved thelarche & menarche after 5 months of treatment. The genomic DNA of the patient, affected siblings and parents were extracted from the whole blood using column based extraction method QIAmp® DNA Blood Mini Kit (Qiagen, Hilden, Germany) according to manufacturer’s protocol. Exome sequencing for genetic analysis was performed on DNA sample from the proband on Illumina NovaSeq platform using TWIST Comprehensive Human Exome Capture Kit hg38. Exome sequencing data analysis revealed novel variant in gene FGFR1:c.1246A > T (NM_023110.3). This variant results in gain of stop codon (null variant) in FGFR1:p.Lys416Ter present at 9th exon of FGFR1. This variant is not present in any publically available databases or in-house database. According to ACMG classification, FGFR1:c.1246A > T is likely pathogenic variant due to absence in publically available database (MAF = 0) and variant is a null variant where FGFR1 is sensitive to haploid sufficiency. This variant causes termination of protein at 416 amino acid, whereas the complete protein is of 822 amino acids. We examined the family for segregation analysis by Sanger sequencing. We identified that proband along with 2 affected siblings was heterozygous for FGFR1 variant. Father was homozygous wild type and mother was heterozygous for FGFR1 variant [Fig. 1a, 1b, 1c shows the clinical features of 1st sister, Fig. 1d shows the pedigree chart and sanger chromatogram in family].

Fig. 1.

A, B, C Clinical photographs of proband presenting ptosis of the left eye and poor dentition (lateral incisors/canines are absent) and syndactyly of the right toes. D Pedigree of the family with three affected female siblings and Sanger chromatogram in the family

Discussion

IHH is a rare disorder with an incidence of 1–10 in 100,000 live births, with approximately two-thirds of cases being due to Kallmann syndrome, which has been mapped to the ANOS1 (previously called KAL1) and fibroblast growth factor receptor 1 (FGFR1) gene mutations. The inactivating mutations of GnRH receptor is the most frequent cause in familial cases as seen in our case [2]. In IHH, along with failure to achieve puberty associated with wide spectrum of symptoms depending upon which gene mutation is responsible among the 25 variant genes. Hypogonadotropic hypogonadism is characterized by insufficient secretion of pituitary gonadotropins resulting in delayed puberty because of anovulation in females and azoospermia in males depending on the mutated gene.

Here we report the result of exome sequencing in the proband presented with classical features of IHH. We identified a novel null variant in FGFR1 gene, c.1246A > T leading to amino acid 416 Lysine to Termination codon. This premature termination codon in the 9th exon of FGFR1 leads to loss of C-terminal protein kinase domain. Sanger segregation analysis also demonstrated heterozygous status in all three affected siblings. The mother, despite carrying the same heterozygous FGFR1 mutation as her affected daughters, exhibited normal fertility. This phenomenon, termed reduced penetrance, has been documented in other families with IHH/KS caused by FGFR1 mutations. These observations within and across families highlight the remarkable disconnect between genotype and phenotype, suggesting a complex interplay within the fibroblast growth factor signaling pathway during the development of the gonadotropin-releasing hormone (GnRH) system. Further research is warranted to elucidate the underlying mechanisms and the potential variability within this signaling network.

A similar case was reported by Sagi SV et al. in two siblings where the GNRH1 gene was responsible for the pubertal failure and in our case we found FGFR1 gene mutations. In both cases, there was a lack of spontaneous onset of puberty where the female presented with primary amenorrhea and the male presented with delayed puberty and small testis and micropenis inherited from both parents [3]. Though the main symptom is the failure of puberty, other abnormalities can be noted similar to our case like absent lateral canines and syndactyly of the toes, and hence IHH is usually diagnosed in late adolescence or early adulthood due to lack of spontaneous pubertal development mainly with complaints of primary amenorrhoea in females. In our case, the whole exome sequencing has revealed FGFR1 pathogenic null variant which is inherited in autosomal dominant pattern. FGFR1 plays pleiotropic roles in human organogenesis including the forebrain, skeleton, and neuroendocrine systems. Also, there can be bone abnormalities as reported by Chelaghma N et al. where the patient having primary amenorrhoea with a low Z score and KISS1R gene mutation was identified [4]. Hormonal therapy with Estrogen and Progesterone to establish the menses and other pubertal symptoms is the mainstay treatment for female patients and there are symptomatic supplementations according to symptoms. These patients can get pregnant but pre-genetic counseling and testing should be done to prevent the suffering of the unborn baby.

The clinically and genetically heterogeneous disorder of IHH with wide variety of genes constantly challenges clinicians and researchers in their efforts to understand the complex molecular genetics of nIHH and KS. Early diagnosis and hormonal therapy with supplemental therapy can prevent negative physical squeal and relieve psychological stress with the restoration of puberty and fertility in affected individuals.

Authors contribution

AG did complete workup of the patients. AK and AD performed the genetic test for the patients. AK and AD performed the genetic test for the family and identified the variant. Post test genetic counselling was done by AG and NG. AG and AK wrote the primary draft. AD and SM reviewed and edited the manuscript. MD and NG did the review of literature for the manuscript.

Funding

There is no funding for this paper.

Declarations

Conflict of interest

There is no conflict of interest among authors.

Informed consent

A written informed consent was taken from the patient to submit her de-identified images.