Pathogenic Yield of Genetic Testing in Autism Spectrum Disorder

Among toddlers with ASD who have pathogenic genetic findings (12%), further medical recommendations were made in 72%. Phenotype fails to predict those with pathogenic findings.

Abstract

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DOI: 10.1542/6176781640001

Video Abstract

BACKGROUND AND OBJECTIVES:

Genetic testing is recommended for individuals with autism spectrum disorder (ASD). Pathogenic yield varies by clinician and/or patient characteristics. Our objectives were to determine the pathogenic yield of genetic testing, the variability in rate of pathogenic results based on subject characteristics, and the percentage of pathogenic findings resulting in further medical recommendations in toddlers with a Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition diagnosis of ASD.

METHODS:

We conducted a retrospective chart review of 500 toddlers, 18 to 36 months, diagnosed with Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition ASD (mean age: 25.8 months, 79% male). Subject demographics, medical and neuropsychological characteristics, and genetic test results were abstracted. Genetic results were divided into negative or normal, variants of unknown significance, and pathogenic. Subject characteristics were compared across results. Manual chart review determined if further recommendations were made after pathogenic results.

RESULTS:

Over half of subjects (59.8%, n = 299) completed genetic testing, and of those, 36 (12.0%) had pathogenic findings. There were no significant differences in Bayley Scales of Infant Development cognitive (P = .112), language (P = .898), or motor scores (P = .488) among children with negative or normal findings versus a variant of unknown significance versus pathogenic findings. Medical recommendations in response to the genetic finding were made for 72.2% of those with pathogenic results.

CONCLUSIONS:

Our findings reinforce the importance of genetic testing for toddlers diagnosed with ASD given the 12% yield and lack of phenotypic differences between subjects with and without pathogenic findings. The majority of pathogenic results lead to further medical recommendations.

What’s Known on This Subject:

Genetic testing (chromosomal microarray and fragile X) is recommended for patients with autism spectrum disorder (ASD). Reported pathogenic yield is 10% for chromosomal microarray and 1to 5% for fragile X. The pathogenic yield in toddlers diagnosed with ASD is unknown.

What This Study Adds:

In a clinical sample of 500 toddlers with Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition ASD, 299 (59.8%) completed genetic testing, and of those, 36 (12.0%) had pathogenic findings. Pathogenic findings impacted medical decision-making 72.2% of the time.

Autism spectrum disorder (ASD) is marked by deficits in social communication and the presence of restricted and repetitive behaviors.¹ ASD is heritable, with a high rate of concordance of diagnoses in monozygotic twins and increased rates among siblings.^2–4 Certain genetic syndromes have an increased rate of co-occurring ASD, including fragile X, tuberous sclerosis, and Rett syndrome, among others. However, these known disorders account for a small proportion of overall ASD cases.^5–8 The American College of Medical Genetics guideline recommends chromosomal microarray (CMA) for all patients with ASD and fragile X testing in boys.⁹ These recommendations were based on reported pathogenic yield for these tests, ∼10% for CMA and 1% to 5% for fragile X.⁹ Although the percentages are not high, the yield is relatively high for a behaviorally diagnosed disorder without a clear biomarker or diagnostic test. In the American Academy of Pediatrics 2019 ASD clinical guidelines, genetic testing is recommended for all children with ASD.

Variation in pathogenic yield is dependent on several factors, including age, with toddlers demonstrating lower yield compared with other age groups.^10–14 Patients with the narrow, more-severe presentation of autistic disorder have higher yield compared with broader ASD phenotypes within the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition.^11,13 Whether yield has changed after changes in the ASD diagnostic criteria remains to be determined. Previous work suggests that yield, particularly for pathogenic de novo mutations, is higher in patients with “syndromic” or “complex” ASD, describing individuals with ASD and features such as intellectual disability, dysmorphism, or congenital anomalies.^{4,5,12,14–16} However, researchers of some studies found no significant differences when comparing medical and neuropsychological features between patients with versus without pathogenic findings.^{4,5,12,14–17}

Despite clinical recommendations to complete genetic testing in individuals with ASD, insurance coverage varies. Although public insurers often reimburse fully for testing, private insurer reimbursement is variable, with testing completely covered, not covered, or covered in a limited manner, resulting in out-of-pocket expense for families. Variation in insurance coverage may occur because little is known about how often a pathogenic finding results in further clinical recommendations. Determining the rate at which genetic findings result in further medical recommendations would improve clinician and patient understanding of potential outcomes after pathogenic results. Should further recommendations be frequent, this would support the current guidelines for testing, inform clinical care, and encourage third-party payer support for coverage of genetic testing in this population. To our knowledge, there are no studies that report the rate at which further medical recommendations are made on the basis of pathogenic genetic results. Our objectives in this study are to understand differences between those who do and do not complete genetic testing, determine the pathogenic yield of genetic testing in a clinical sample of toddlers with a Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) diagnosis of ASD, compare medical and neuropsychological characteristics among patients with differing genetic findings (normal or no pathogenic finding versus variant of unknown significance versus pathogenic), and determine the rate at which pathogenic findings result in subsequent medical recommendations.

Methods

Sample

We conducted a retrospective chart review of 500 toddlers (18–36 months) with an ASD diagnosis made in the Developmental Medicine Center at Boston Children’s Hospital (BCH) via an interdisciplinary team assessment from July 1, 2013, to May 1, 2016. Five children were excluded because they were seen by a single clinician, rather than a team, for the initial ASD evaluation. In the team assessments, a developmental-behavioral pediatrician obtained a medical and developmental history and conducted a physical examination and a clinical child psychologist obtained neuropsychological measures. Diagnoses were formulated and agreed on by the pediatrician and psychologist through a clinical team meeting that occurred immediately after the diagnostic assessment and through which consensus diagnoses were made. The Bayley Scales of Infant and Toddler Development, Third Edition (Bayley)¹⁸ was used to obtain cognitive, language, and motor standard scores. The Vineland Adaptive Behavior Scales, Second or Third Editions^19,20 were used to obtain scores related to adaptive functioning. The time frame for data abstraction corresponded with a clinic-wide shift to use of a checklist to ensure fidelity to the new DSM-5 criteria.²¹ We identified subjects via electronic medical record search based on a billing code signifying a team assessment (99245 AND 96118 or 96119) and an International Classification of Diseases, Ninth Revision or 10th Revision code for ASD (F84.0, F84.9, or F84.5 or 299.0, 299.8, or 299.9). Inclusion criteria were a documented DSM-5 diagnosis of ASD made via a team assessment. Patients are referred to the center by primary care clinicians, early childhood intervention providers, or parents on the basis of concern for delayed or atypical development. It is standard practice for clinicians in this practice to recommend genetic testing (CMA and fragile X) for all children diagnosed with ASD. The study was approved by the BCH Institutional Review Board with a waiver of informed consent.

Data Collection Procedures

We abstracted demographic, medical, and neuropsychological information for all subjects (Table 1). We recorded whether subjects completed genetic testing, along with the results of all CMA and fragile X testing. CMA analysis was performed via custom whole genome array with enhanced probe coverage on targeted genes and with single nucleotide polymorphism or loss of heterozygosity probes (Optimized Version 3.0 on Agilent 180k platform). The array uses human genome build 19, has a resolution of ∼50 kb for targeted regions or genes, and can detect copy number changes as small as ∼150 kb between targeted regions. CMA findings were reported as follows: (1) no clinically significant copy number variants or areas of copy number neutral homozygosity (≥10 Mb) were identified (which we refer to as “negative or normal”), (2) variants of unknown or uncertain significance, and (3) known or likely pathogenic finding. For fragile X testing, DNA was amplified across the region of CGG repeats in Fragile X mental retardation 1 by using Asuragen Amplidex Fragile X mental retardation 1 polymerase chain reaction reagents. Fragile X results were reported by CGG repeats, categorized as (1) normal (5–44 repeats), (2) “grey zone” (45–54 repeats), (3) premutation (55–200 repeats), and (4) full mutation (>200 repeats). All tests were performed at Claritas Genomics and followed the requirements of Clinical Laboratory Improvement Amendment 88 for clinical testing. Analyses were performed on DNA extracted by standard methodologies from blood samples. Results were reviewed, and the pathogenicity of those results determined by laboratory geneticists with Claritas Genomics. Pathogenicity determination was included in the report that was returned to the ordering clinician who, in turn, communicated the results to the parent. For pathogenic findings, clinicians often referred to a geneticist who then made additional, specific recommendations. For purposes of analyses, we considered known or likely pathogenic CMA findings and any abnormal fragile X findings to be “pathogenic.”

TABLE 1.

Variables Abstracted From Medical Record

Demographic Characteristics	Medical Characteristics	Neuropsychological Characteristics
Age at diagnosis	Gestational Age	Verbalb or nonverbal
Sex	Regressionc	Bayley cognitive standard score
Insurance	Epilepsy	Bayley language standard score
Mean household incomea	Head Circumference	Bayley motor standard score
	Family history of ASD	Vineland adaptive behavior composite
	Dysmorphic features reported by clinician	Vineland communication standard score
	Hypotonia	Vineland motor standard score
	Additional diagnosis of global developmental delay (Bayley cognitive standard score <70)	Vineland socialization standard score

To evaluate the potential biased effects of missing data, a series of tests evaluated whether missing data participants (on the dependent variables) were disproportionally allocated to the two groups of interest (genetic testing or not). Results found by using a series of χ² tests pointed to the adoption of null hypotheses only. Consequently, the amount of missing data were approximately equally distributed across individuals with genetic testing scores and without. The interested reader may consult Supplemental Information.

^aEstimated via census tracts based on subject zip code at diagnosis.

^bAt least 1 consistent, recognizable word.

^cClinician concern for regression which was indicated by referral to a subspecialist (neurology or metabolism and/or genetics) or further metabolic laboratory studies.

For patients with a pathogenic CMA finding, we performed further manual chart review to determine if a medical recommendation was subsequently made on the basis of the genetic result. The following documented medical recommendations would not have otherwise been made before the return of a pathogenic result: referral to other specialists (endocrinology, metabolism, and sleep medicine in our sample), audiology examination, ophthalmology examination, monitoring for seizures, echocardiogram, renal ultrasound, or other laboratory evaluation (urine amino acids, creatine kinase level). For pathogenic CMA results, referral to genetics, parental testing, or genetic counseling were not considered a recommendation. Those with a pathogenic finding on fragile X testing were referred to a fragile X clinic. This was considered a further medical recommendation because this referral informed family planning and resulted in ongoing monitoring. Although genetic testing is recommended at the time of diagnosis, factors such as family preference, logistics, and insurance authorization often delay testing. Data abstraction occurred at least 2 to 3 years after the diagnosis of ASD and thus reflects any genetic testing that occurred following the ASD diagnosis. Two trained reviewers (including author H.H.) recorded data in the Research Electronic Data Capture (REDCap)²² database with >96% interrater reliability as determined by bimonthly review of 10% of the records that were double-coded. A third reviewer (E.H.) arbitrated any coding discrepancies.

Statistical Analyses

We calculated frequencies and percentages to represent the baseline characteristics of the sample. We used independent sample t tests to evaluate for significant differences between patients who completed versus did not complete genetic testing on continuous variables and χ² tests for categorical variables. Power levels were in excess of 99% for either test (Supplemental Information). Effect sizes involved Glass δ statistic, which is a variant of Cohen d, for which values of 0.2, 0.5, and 0.8 are indicative of small, medium, and large effects, respectively. In hypotheses involving percentages, χ² statistics were also presented with this effect size metric by using SDs. Thus, effects are comparable across all tests.

Results

Among subjects in the study (N = 500, 79.2% male), 299 (59.8%) completed genetic testing (mean age: 25.8 months at diagnosis). There were no differences in demographic characteristics between those children that completed genetic testing versus those that did not (Table 2). Subjects who completed testing were more likely to have dysmorphic features, be nonverbal, and have lower Bayley language scores and lower scores on parent report of overall adaptive functioning, communication, motor, and socialization skills (Table 2).

TABLE 2.

Comparison Between Subjects Who Completed Genetic Testing and Patients Not Completing Genetic Testing Across Demographic and Medical Characteristics

	Patients Completing Genetic Testing (n = 299)	Patients Not Completing Genetic Testing (n = 201)	Statistica	Pa	Effect Sizeb
Demographic characteristics
Age (mean, SD)	25.84 (4.4)	26.21 (4.5)	0.92	.36	−0.08 (–0.26 to 0.10)
Female, n (%)	65 (21.7)	39 (19.4)	0.40	.53	0.12
Insurance, n (%)			3.03	.22	0.16
Private	164 (54.9)	126 (62.7)
Public	126 (42.1)	70 (34.8)
Other	9 (3.0)	5 (2.5)
Mean income	85 077.82	82 889.39	0.69	.49	0.06
Medical characteristics, n (%)
Premature (GA ≤36)	64 (21.4)	48 (23.9)	0.42	.52	0.12
Regression	14 (4.7)	6 (3.0)	0.90	.34	0.43
Epilepsy	3 (1.0)	3 (1.5)	0.24	.62	0.41
Family history of ASD	89 (29.8)	57 (28.4)	0.12	.73
Dysmorphic features reported by clinician	21 (7.0)	6 (3.0)	3.84c	.05c,d	0.81
Additional diagnosis of global developmental delay	125 (41.8)	74 (36.8)	0.21	.65	0.07
Neuropsychological characteristics
Verbal, n (%)	160 (53.5)	128 (63.7)	5.09c	.02c	0.27
Bayley cognitive standard score, mean (SD), n	79.77 (14.16), 294	81.81 (14.83), 193	1.53	.13	−0.14
Bayley language standard score, mean (SD), n	61.45 (12.51), 213	65.35 (16.69), 132	2.31c	.02c	−0.23
Bayley motor standard score, mean (SD), n	78.60 (13.86), 212	79.36 (12.10), 135	0.52	.60	−0.06
Vineland adaptive behavior composite, mean (SD), n	73.35 (8.38), 252	76.55 (9.90), 175	3.61c	.001c	−0.32
Vineland communication standard score, mean (SD), n	69.54 (11.89), 264	73.85 (13.61), 180	3.45c	.001c	−0.32
Vineland motor standard score, mean (SD), n	85.57 (10.78), 261	87.62 (9.77), 178	2.04c	.04c	−0.21
Vineland socialization standard score, mean (SD), n	73.28 (7.27), 265	76.62 (9.72), 179	3.92c	.001c	−0.34

^aP values are for independent sample t tests for continuous dependent variables or χ² tests whenever both variables were categorical.

^bEffect size indicators are Glass δ statistic, which is a variant of Cohen d; estimates of 0.2, 0.5, and 0.8, respectively, are indicative of small, medium, and large effects. Estimates for the χ² tests were also transformed on the SD metric, and consequently, Cohen rules apply to them as well.

^cSignifies statistically significant finding with P <.05 when it appears in the absence of footnote “d.”

^dFinding does not exceed levels of significance using the Benjamini–Hochberg correction using a false discovery rate of 0.20.

Of the 299 subjects who completed testing, 186 (62.2%) had negative or normal findings, 77 (25.8%) had variants of unknown significance on CMA, and 36 (12%) had a pathogenic finding (Fig 1). Of those with pathogenic findings, 27 subjects had pathogenic variants on CMA (9.0%) and 9 subjects had pathogenic fragile X findings (3.0%). The most common copy number variants in this sample were deletions or duplications on 15q (n = 10) and 22q (n = 2). Among subjects with fragile X findings, there were 3 full mutations, 3 premutations, 2 intermediate or “grey zone” mutations, and 1 patient with mosaicism (Table 3). The role of fragile X premutations, “grey zone” mutations, and mosaicism in ASD is an ongoing area of investigation. Because current literature suggests potential relevance, we considered these mutations pathogenic.^23–25

FIGURE 1.

Flowchart breakdown of genetic testing completion, results, and subsequent action.

TABLE 3.

Pathogenic Findings

Genetic Findings in Sample According to Test Performed	n (%)
CMA completed	299
Variants of unknown significance	77 (25.8)
Known pathogenic or likely pathogenic finding	27 (9.0)
15q deletions or duplications	10
22q11 deletions or duplications	2
The remaining were found in a single patient:	1
48 XXYY
Mosaic trisomy 8
1p12 deletion
2p21 deletion
2p22.3-22.2 deletion
2q12.3-q13 deletion
2q37.3 deletion
4q21.21 deletion
5p15.33-p15.31 deletion
5q11.2-13.1 deletion
8p22 deletion
13q32.3 deletion
16p13.11 deletion
20p11.23-p11.21 deletion
Xp21.1 duplication
Fragile X test completed	299
Positive finding	9 (3.0)
Full mutation	3
Premutation	3
Gray zone	2
Mosaic	1

There were no significant differences in cognitive, language, or motor standard scores or in patient age, insurance, or median household income across genetic result categories (Table 4). Among subjects who completed genetic testing, there was a higher rate of variants of unknown significance for girls versus boys (25 of the 65 girls, 38.5%; compared with 52 of the 234 boys, 22.2%; P = .03). There was a significant difference in mean motor standard score on the Vineland Adaptive Behavior Scales across genetic finding categories (86.54 for negative or normal finding, 85.60 for variants of unknown significance, and 80.10 for pathogenic findings; P = .01).

TABLE 4.

Comparison Between Subjects With Pathogenic Findings, Variants of Unknown Significance, and Normal Results

	G1: Negative or Normal Results (n = 186)	G2: Variant of Unknown Significance (n = 77)	G3: Known Pathogenic Finding (n = 36)	Statistica	Pa	Effect Sizeb G1 Versus G2	Effect Sizeb G1 Versus G3	Effect Sizeb G2 Versus G3
Demographic characteristics
Age, mean (SD)	25.78 (4.5)	26.35 (4.1)	25.03 (4.5)	1.13	.33	−0.13	0.17	0.29
Female (n = 65, 21.7%), n (%)	32 (49.2)	25 (38.5)	8 (12.3)	7.15c	.03c	0.32	0.32	0.32
Male (n = 234, 78.3%), n (%)	154 (65.8)	52 (22.2)	28 (12.0)	—	.03c	0.32	0.32	0.32
Insurance				11.07	.20	0.42	0.42	0.42
Private, n (%)	101 (43.3)	40 (51.3)	23 (65.7)	—	—	—	—	—
Public, n (%)	81 (43.5)	33 (42.3)	12 (34.3)	—	—	—	—	—
Other, n (%)	4 (2.2)	5 (6.4)	0 (0.0)	—	—	—	—	—
Mean income	84 630.11	92 605.44	88 192.85	1.65	.19	−0.23	−0.11	0.14
Medical characteristics, n (%)
Premature (GA ≤36)	44 (23.7)	15 (19.2)	5 (14.3)	1.83	.40	0.34	0.34	0.34
Regression	9 (4.8)	2 (2.6)	3 (8.6)	1.98	.37	0.78	0.78	0.78
Epilepsy	3 (1.6)	0 (0.0)	0 (0.0)	1.84	.40	2.52	2.52	2.52
Family history of ASD	53 (28.5)	29 (37.2)	7 (20.0)	3.79	.15	0.45	0.45	0.45
Sibling with ASD	17 (9.1)	5 (6.4)	5 (14.3)	3.83	.43	0.81	0.81	0.81
Dysmorphic features reported by clinician	9 (4.8)	7 (9.0)	5 (14.3)	4.64	.10	1.07	1.07	1.07
Diagnosis of global developmental delay	79 (42.5)	28 (35.9)	18 (51.4)	4.05	.40	0.37	0.37	0.37
Diagnosis of hypotonia	8 (4.3)	4 (5.1)	1 (2.9)	4.27	.37	1.40	1.40	1.40
Neuropsychological characteristics
Verbal, n (%)	99 (53.2)	47 (60.3)	14 (40.0)	4.00	.14	0.32	0.32	0.32
Bayley cognitive standard score, mean (SD), n	80.47 (14.34), 184	80.20 (13.75), 76	75.00 (13.60), 34	2.21	.11	0.02	0.40	0.38
Bayley language standard score, mean (SD), n	61.37 (13.05), 135	62.04 (11.70), 52	60.69 (11.53), 26	0.11	.90	−0.06	0.06	0.12
Bayley motor standard score, mean (SD), n	79.24 (14.18), 133	78.47 (13.05), 51	75.79 (13.90), 28	0.72	.49	0.06	0.25	0.19
Vineland adaptive behavior composite, mean (SD), n	73.68 (8.01), 154	74.01 (9.27), 70	69.89 (7.42), 28	2.76	.07	−0.04	0.51	0.56
Vineland communication standard score, mean (SD), n	69.60 (11.45), 162	70.68 (13.42), 73	66.28 (9.79), 29	1.44	.24	−0.08	0.34	0.45
Vineland motor standard score, mean (SD), n	86.54 (10.43), 160	85.60 (11.19), 72	80.10 (10.39), 29	4.50c	.01c	0.08	0.62	0.53
Vineland socialization standard score, mean (SD), n	73.04 (6.85), 163	73.52 (8.11), 73	74.00 (7.57), 29	0.27	.76	−0.06	−0.13	−0.06

^aP values are for one-way analyses of variance comparisons when dependent variables were continuous; for qualitative variables, χ² tests were used.

^bEffect size indicators are in Cohen d metric (ie, SD units) with values of 0.2, 0.5, and 0.8 being indicative of small, medium, and large effects. χ² goodness of fit values were also transformed onto Cohen d metric. In the presence of 1 effect size, findings refer to the overall (omnibus) test statistic.

^cSignifies statistically significant P <.05.

Of those children with a pathogenic finding (n = 36), manual chart review was conducted to determine if a medical recommendation was made on the basis of the finding. All children with positive fragile X results (n = 9) received a further recommendation via referral to a fragile X clinic for genetic counseling and comprehensive care. Of subjects with pathogenic CMA findings (n = 27), 17 children (63%) had a medical recommendation made on the basis of their finding(s). The most common medical recommendations included education regarding risk and management of potential seizures and seizure monitoring (n = 5) and referrals to subspecialists (endocrinology, metabolism, or sleep medicine; n = 4). Other common recommendations included echocardiogram, renal ultrasound, audiology examination, and ophthalmology examination (n = 3 for each). In summary, including both pathogenic CMA findings and positive fragile X findings, 26 of 36 subjects (72.2%) had subsequent medical recommendations made on the basis of their results.

Discussion

In this study, 59.8% of toddlers with a DSM-5 diagnosis of ASD completed genetic testing. Many factors may influence completion rate, including clinician practices or family considerations such as the likelihood of a positive result, the potential for results with unclear significance, or family planning implications. Additional barriers include discomfort of phlebotomy, cost, and third-party payer policies. Although the rate of completed testing in our sample is higher than previously reported (parent surveys report rates of 28%–41%), it is low in the context of guidelines that recommend genetic testing in all patients with a new ASD diagnosis.^26,27 In this sample, parents’ likelihood to pursue genetic testing for their child did not vary on the basis of subject age, insurance status, sex, or median household income. Patients who had dysmorphic features, were nonverbal, and had lower language scores were more likely to complete testing. Additionally, for those children completing testing, parent report across domains of functioning (adaptive, communication, motor, social) was lower compared with children who did not complete testing.

Among subjects who did complete CMA and fragile X testing, the pathogenic yield of 12.0% is consistent with previous reports.^9,14,28 We did not find significant differences in age at diagnosis, insurance status, or median household income between those with and without pathogenic findings. There was a higher percentage of female subjects in the group with variants of unknown significance. This finding may be consistent with the hypothesis that girls require a higher burden of mutations to reach a threshold required to manifest ASD, known as the female protective effect.²⁹ Ho et al¹⁵ also demonstrated a higher rate of pathogenic mutations in female patients with complex ASD.

There were no differences in medical characteristics of interest, nor was there a statistically significant difference in Bayley cognitive scores across subjects in the 3 categories of genetic test results (normal or negative findings, variants of unknown significance, and pathogenic findings). This finding is in contrast to previous work suggesting a higher pathogenic yield of testing in complex ASD, which often includes intellectual disability or cognitive delay, but is consistent with a recent study by McGrew et al,¹⁷ who compared characteristics between children with and without pathogenic findings and found no differences.^10,12,14 Although measuring cognitive functioning in young children is challenging, our results suggest that clinicians should continue to recommend genetic testing regardless of cognitive level.

In our sample, children with known pathogenic findings had lower parent-reported motor functioning than children with negative or normal results or variants of unknown significance. This raises the question of the role of motor delays in suggesting a potential underlying genetic etiology, an area of recent investigation.³⁰ However, although this difference was statistically significant in our sample, scores in both groups remained in the “low adequate” to “moderately low” range on the Vineland Scales; such differences may not be appreciable clinically.

In children with pathogenic CMA or fragile X findings, 72.2% had further medical recommendations made on the basis of their genetic results. We combined fragile X and CMA when reporting on percentage receiving medical recommendations given our focus on implications of genetic testing in ASD overall. All subjects with abnormal fragile X results received referral to a genetic specialist. For CMA alone, 17 of 27 (63%) received medical recommendations. Additionally, all patients with a pathogenic finding received genetic counseling around family planning. When considering the entire group of subjects (N = 299) who completed genetic testing, 8.7% had a medical recommendation made on the basis of their results. This finding is consistent with one previous report of 6.2%.¹⁴ Our results suggest that genetic test findings do not merely provide information for families but also result in further medical recommendations and monitoring, arguing for broader, more uniform third-party payer coverage. Furthermore, a pathogenic genetic finding may provide an answer for families seeking to understand why their child has ASD.

A potential limitation to this study is our retrospective methodology; thus, data are limited to information documented in the medical record. For example, some demographic information (race, ethnicity, maternal education) was not routinely collected. All genetic testing available for review was performed at the BCH laboratory. It is possible that some children may have had genetic testing conducted at other approved laboratories and that these results were not documented in their medical records. Although all clinicians within the practice are instructed to recommend testing and documented such recommendations in the note, the strength with which the recommendation was communicated verbally cannot be confirmed. Only 60% of subjects completed genetic testing, and on the basis of our comparisons, it is possible that the perception of greater impairment on the part of parent and/or clinician increased the likelihood that a patient completed testing, which could have influenced our findings; however, differences between those who did versus did not complete testing were unlikely to be clinically important, as indicated with effect sizes being below an accepted medium-level threshold.³¹ Of the sample that did ultimately complete testing, there were no significant differences in medical characteristics or objectively measured cognitive, language, or motor functioning between subjects across result categories. We used billing and diagnostic codes to identify cases, and thus there is the potential for false-negatives (children who have ASD were not billed in this manner), although this would be highly unlikely because toddlers are usually presenting for the first time, evaluated through the team assessment, and billed as such. The study sample comes from a single tertiary care site. However, the majority of children in our region with a concern for ASD are referred to a tertiary center for developmental evaluation because this is the means to access services. Thus, we believe our sample is representative of young children receiving a diagnosis of ASD in our region. Although our sample size is large, the number of children with pathogenic genetic findings is small (n = 36) and must be considered when evaluating the frequency with which medical recommendations are made within this group. A strength of the study is the large sample size of toddlers with a DSM-5 diagnosis. Additionally, the standardized format of the comprehensive interdisciplinary team visit allowed us to evaluate numerous medical and neuropsychological characteristics for the sample.

Conclusions

In a clinical sample of toddlers with DSM-5 ASD, almost 60% completed genetic testing (CMA and/or fragile X). Of those who completed genetic testing, 12% had a pathogenic finding. There was no association between medical characteristics or cognitive, language, and motor functioning and the likelihood of a pathogenic finding. Our results suggest that genetic testing (CMA and/or fragile X) should continue to be recommended for patients receiving a diagnosis of ASD, regardless of phenotypic characteristics at diagnosis. Further medical recommendations were made in 72.2% of patients with pathogenic findings, indicating that genetic testing in this population has significant clinical implications. With these findings, we highlight the importance of genetic testing for toddlers with a diagnosis of ASD.

Glossary

ASD

autism spectrum disorder

Bayley

Bayley Scales of Infant and Toddler Development, Third Edition

BCH

Boston Children’s Hospital

CMA

chromosomal microarray

DSM-5

Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition

REDCap

Research Electronic Data Capture