What is the risk of my child developing autism given the family history?

Risk of Autism in Siblings of Individuals with Autism Spectrum Disorder

If you have a brother with autism, your child has approximately a 14-18% chance of developing autism spectrum disorder (ASD), which is significantly higher than the general population risk of about 1-2%. 1

Genetic Basis and Recurrence Risk

The elevated risk for autism in siblings is well-established in multiple studies:

• According to data from a US registry of 2,920 children in families affected by ASD, the frequency of ASD in later-born siblings is estimated at 14% 1
• More recent prospective longitudinal research involving infant siblings of children with ASD reported a pooled estimated recurrence risk of 18% 1
• Some population registry-based studies from Denmark have estimated a somewhat lower recurrence risk of 7-8% 1

Regardless of the exact percentage, all evidence confirms that rates of ASD in siblings greatly exceed the general population risk of approximately 1-2% 2.

Factors Influencing Risk

The risk for autism has a strong genetic component:

• Twin studies have reported 60% concordance for classic autism in monozygotic twins versus 0% in dizygotic twins 3
• When evaluating for broader autism phenotype (including milder communication and social disorders), concordance increases to 92% in monozygotic twins and 10% in dizygotic pairs 3
• Current evidence suggests that "idiopathic" autism (cases without a known single genetic cause) results from interactions between multiple genes 3

Recommendations for Monitoring

Because of this elevated risk, children with siblings who have ASD require intensified developmental surveillance:

• At minimum, these children should receive continuous surveillance for developmental issues 1
• They should be specifically screened for ASD at 18 and 24 months of age, as recommended by the American Academy of Pediatrics 1
• Parents should be vigilant for early signs of ASD in the first two years of life, including:
  • No response to name when called
  • No or limited use of gestures in communication
  • Lack of imaginative play 2
  • Decreased social gaze, social smiles, and vocalizations between 6-18 months 1
  • Atypical use of objects (spinning, lining up, rotating) as early as 12 months 1

Early Detection and Intervention

Early identification is critical as it leads to earlier intervention, which improves outcomes:

• Parental reports of decline in play and communication and impaired vocal imitation at 12 months can help identify ASD in high-risk siblings 4
• Children identified through ASD-specific screening should be immediately referred for diagnostic evaluation and appropriate intervention 1
• Early intervention services may include speech therapy and early childhood education programs 1

Important Considerations

• The diagnostic stability of ASD in children diagnosed after 24 months is well-established 1
• Emerging evidence suggests that ASD diagnoses in children identified before 24 months can also be stable, though more research is needed 1
• Not all siblings of children with ASD will develop the condition, but they may show milder features of the broader autism phenotype 3

Early recognition and intervention are key to improving outcomes for children at increased risk of ASD, making regular developmental monitoring essential for families with a history of autism.