Autism runs in families: 1 in 5 children with older siblings with autism will be autistic

In the past decade, autism prevalence has increased to 1 in 36, which may reflect work to improve autism spectrum disorder diagnosis, particularly of autistic females.

A new study in the August 2024 Pediatrics, “Familial Recurrence of Autism: Updates from the Baby Siblings Research Consortium,” found that children with an older sibling with autism are much more likely to be diagnosed with autism (1-in-5).

Researchers examined data of 1,605 infants with an older sibling with autism spectrum disorder in the Baby Siblings Research Consortium database, composed of studies from across the US and around the world, and found 20.2 percent of younger siblings of children with autism spectrum disorder would be themselves diagnosed with autism. This replicated an earlier study done in 2011 which found a similar rate of familial recurrence.

Many factors contributed to greater odds of autism in the younger sibling. Younger siblings of females with autism spectrum disorder were significantly more likely to develop autism spectrum disorder (34.7 percent) than siblings of boys (22.5 percent), while male younger siblings were more likely to have autism spectrum disorder than girls (25.3 percent compared to 13.1 percent).

Race also influenced the likelihood of recurrence: in white families, autism spectrum disorder recurred in 17.8 percent while across other races as a group the recurrence rate was 25 percent. Maternal education was also important; recurrence was 32.6 percent when mothers attained high-school or less education; some college, 25.5 percent; college degree, 19.7 percent; and graduate degree, 16.9 percent. When a baby had more than one older sibling with autism, the recurrence rate rose to 36.9 percent.

Study authors concluded that the rate of autism is seven times higher in families who already have one autistic child than in the general population, which emphasizes the need for close developmental surveillance of new infants in those families. This information may be useful to families in planning for and supporting future children and in improving access to earlier screening and interventions for autism in young children.

The American Academy of Pediatrics is an organization of 67,000 primary care pediatricians, pediatric medical subspecialists and pediatric surgical specialists dedicated to the health, safety and well-being of infants, children, adolescents and young adults.

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