What are the chances of having another child with Autism Spectrum Disorder (ASD) in a family with a history of autism?

Recurrence Risk of Autism Spectrum Disorder in Siblings

The risk of having another child with autism depends critically on your family composition: if you have one affected male child, the risk for a subsequent female child is approximately 10%, while for a subsequent male child it is higher; if you already have two affected children, the recurrence risk jumps dramatically to 32-50%. 1

Risk Stratification Based on Family Composition

Single Affected Child

• If your first affected child is male: The risk for the next male child is approximately 7-10%, while the risk for the next female child is approximately 4-10% 1
• If your first affected child is female: The recurrence risk is higher for subsequent children (both male and female) because female probands indicate a higher genetic load 1
• Population-based data suggests: An average recurrence risk of approximately 6% across all siblings, though prospective studies of high-risk families report rates of 11-19% 1

Multiple Affected Children

• If you already have two or more children with ASD: The recurrence risk escalates dramatically to 32-50% for any future pregnancy 1
• Specifically with two affected boys: A mother faces a 32% risk that the next male child will have autism 1

Understanding the Wide Risk Range

The variation in reported recurrence risks (6-32%) reflects several important factors:

• Ascertainment bias: Studies recruiting from autism clinics tend to report higher recurrence rates (11-19%) compared to population-based registries (6%) because families with multiple concerns are more likely to enroll 1
• Genetic heterogeneity: ASD results from interactions of at least 10 different genes, meaning different families carry different genetic risk profiles 1
• Sex-specific protective factors: Females appear to have protective factors that reduce ASD risk, explaining why affected females signal higher familial risk 1

Clinical Implications and Genetic Testing

I strongly recommend genetic evaluation for your affected child, as this provides the most accurate recurrence risk counseling for your specific family:

• Chromosomal microarray analysis yields clinically relevant genetic findings in 40% of children with ASD 1
• Clinical exome sequencing adds an additional 15-25% diagnostic yield if initial testing is negative 1
• When a specific genetic cause is identified: Recurrence risk counseling becomes precise rather than empirical, and targeted testing of future pregnancies becomes possible 1

Important Caveats About Genetic Testing

• Most ASD-associated genetic variants occur de novo (spontaneously) rather than being inherited, so negative genetic testing in your affected child does not eliminate recurrence risk 2
• If no genetic cause is identified, the empirical recurrence risks listed above apply 1, 2
• Specific genetic findings (such as 15q11-13 duplications or 16p11.2 deletions) also inform you about associated medical risks like epilepsy, intellectual disability, and motor impairment that require screening 1

Comparison to General Population Risk

For context, the baseline population risk without any family history is approximately 1-1.6% (1 in 60-160 children) 2. Your recurrence risk of 6-32% represents a 4-fold to 20-fold increase above this baseline, confirming the strong genetic component of ASD 1, 3.

Heritability Evidence

Twin studies demonstrate 70-90% concordance in monozygotic twins versus only 3-10% in dizygotic twins, and recent large-scale Swedish population studies estimate ASD heritability at approximately 50% 1, 3. This means that while genetics play a major role, environmental and epigenetic factors also contribute to whether ASD manifests 3.