Investigation and Approach for Autistic Patients
All patients with confirmed autism spectrum disorder should undergo a tiered genetic and medical evaluation, with genetic consultation offered to all families, as this approach yields an etiologic diagnosis in 30-40% of cases and directly impacts medical management, family counseling, and preventative health strategies.
Pre-Evaluation Requirements
Before initiating any genetic workup, several critical steps must be completed 1:
- Confirm ASD diagnosis by a trained professional using objective criteria and standardized tools (e.g., Autism Diagnostic Observation Schedule-Second Edition, Autism Diagnostic Interview)
- Formal audiogram is mandatory to rule out significant hearing loss that can mimic ASD symptoms
- Cognitive testing to establish baseline developmental level
- EEG only if clinical suspicion of seizures exists (not routine)
- Verify newborn screening results were normal
First-Tier Investigations (Highest Yield)
Clinical Examination
Perform a detailed physical examination focusing on 2:
- Dysmorphic features suggesting syndromic causes
- Woods lamp examination for hypopigmented macules (tuberous sclerosis)
- Head circumference measurement (macrocephaly suggests specific genetic testing)
Genetic Testing (First-Line)
Chromosomal microarray (comparative genomic hybridization) is now the standard first-line genetic test, with 24% diagnostic yield—significantly higher than traditional karyotype (2.5% yield) 3, 1. This has largely replaced high-resolution karyotype as the initial test.
Fragile X DNA testing should be performed if not already done (0.57% yield but critical to identify) 2, 3.
Conditional Metabolic Screening
Order metabolic tests only if clinical indicators are present (regression, seizures, unexplained developmental plateau) 2:
- Urine mucopolysaccharides and organic acids
- Serum lactate, amino acids, ammonia, acyl-carnitine profile
Do not order routine metabolic screening in the absence of clinical indicators—this represents a common pitfall that increases cost without improving diagnostic yield 1.
Second-Tier Investigations (Targeted Based on First-Tier Results)
Proceed to second-tier testing if first-tier is unrevealing 2:
- MECP2 gene testing in females only (5% yield in females)
- PTEN gene testing if head circumference is ≥2.5 standard deviations above mean (3% yield in macrocephaly)
- Fibroblast karyotype if clonal pigmentary abnormalities noted with normal leukocyte karyotype
Third-Tier Investigations (Specialized)
Reserve for specific clinical scenarios 2:
- Brain MRI when focal neurological signs, regression, or specific syndromic features present
- Serum and urine uric acid with subsequent enzyme testing if abnormal
Tests NOT Recommended for Routine Use
The following have insufficient evidence for routine testing 1:
- CDKL5 testing
- Cholesterol/7-dehydrocholesterol
- Mitochondrial gene sequencing
- Routine neurometabolic screening panels in absence of clinical indicators
Genetic Consultation
Offer genetic consultation to all ASD patients and families 1. The geneticist should:
- Coordinate with primary care physician for test ordering and scheduling
- Provide genetic counseling regardless of whether etiology is identified
- Discuss recurrence risks: 3-10% for siblings (7% if affected child is female, 4% if male; ≥30% if two or more affected children)
Co-occurring Medical Conditions Assessment
Screen for common comorbidities that affect morbidity and quality of life 4, 3:
- Depression (20% prevalence vs 7% general population)
- Anxiety (11% vs 5%)
- Sleep difficulties (13% vs 5%)
- Epilepsy (21% with intellectual disability vs 0.8%)
- ADHD symptoms
Critical Pitfalls to Avoid
- Do not order extensive metabolic panels routinely—only when clinical indicators present (regression, seizures, specific dysmorphic features)
- Do not skip audiogram—hearing loss mimics ASD and must be excluded
- Do not order traditional karyotype alone—chromosomal microarray has superior yield and should be first-line
- Do not delay genetic consultation—30-40% diagnostic yield directly impacts management
- Do not assume negative initial workup is final—periodic re-evaluation as technology advances may yield diagnosis 1
Coordination of Care
Establish a primary care medical home that partners with genetics to coordinate 1:
- Diagnostic test ordering and scheduling
- Management of identified etiologies
- Treatment of co-occurring conditions
- Periodic re-evaluation if initial workup negative
This tiered approach balances diagnostic yield, invasiveness, cost-effectiveness, and practical implementation while maximizing the chance of identifying treatable conditions and providing families with prognostic information.