Two research groups investigate the recurrence rate of autism spectrum disorders in families

Two separate studies are reporting new findings about the familial recurrence rate in autism—that is, the likelihood that siblings of older children with autism spectrum disorders (ASD) will be diagnosed with ASD
themselves.

In the first study, Sally Ozonoff of the UC Mind Institute and her colleagues analyzed data on 1,605 infants with an older autistic sibling. The researchers followed all of the younger siblings from early infancy to three years of age, when they were assessed for ASD. Data were collected at 18 sites in the United States, Canada, and the United Kingdom.

Ozonoff and her team found that the familial recurrence rate for ASD was 20.2%, which is only slightly higher than the rate they found in 2011.

The researchers, who had conducted a similar study in 2011, report, “A total of 20.2% of siblings developed ASD, which is not significantly higher than the previously reported rate of 18.7%.”

Ozonoff and her team found that if the first autistic child in a family was a girl, the parents were 50% more likely to have another child with ASD than if the first autistic child was a boy. She comments, “This points to genetic differences that increase recurrence likelihood in families who have an autistic daughter.” If the younger sibling was a boy, the recurrence rate was 25%, while the rate was 13% if the younger sibling was a girl. Children with multiple autistic siblings had a 37% likelihood of developing ASD.

The researchers also found that children from non-white families and children whose mothers had fewer years of education had higher recurrence rates of ASD. Ozonoff comments, “These findings are new—and critical to replicate. They do mirror the recent CDC findings that autism is more prevalent in children of historically underrepresented groups.”

A second study, by researchers participating in the BASIS/STAARS project in the United Kingdom, reports that the recurrence rate of autism in families increases when siblings are reevaluated in mid-childhood.

Bazelmans and colleagues report that the familial recurrence rate for ASD rises significantly if children are reassessed in mid-childhood.

The study, by Tessel Bazelmans and colleagues, examined data collected on 159 children who had older siblings with autism. Participants underwent diagnostic assessments at three years of age and again in
mid-childhood when they were between six and 12 years of age. The researchers report that the autism recurrence rate in their sample in mid-childhood was 37.1%. They add, “Around half of those diagnosed with autism in mid-childhood had not received a diagnosis at three years.”

The researchers say that children diagnosed with ASD in mid-childhood but not at the three-year assessment were more likely to be girls and to have higher IQs at the earlier assessment. Parents of some children diagnosed in mid-childhood reported that starting school and facing other social challenges made autism characteristics more apparent as their children aged.

The researchers comment, “It is important for parents and carers to know that in younger infant siblings an autism presentation may not always be clear in the preschool years. This will enable them to monitor and recognize the expression of autistic characteristics if they emerge later in development and then to seek advice and support.”

The researchers caution that their study involved a single-site sample of modest size. However, they say their findings have implications for families and clinical services as well as for prospective family history studies.

Citations

“Familial recurrence of autism: updates from the Baby Siblings Research Consortium,” Sally Ozonoff, Gregory S. Young, Jessica Bradshaw, Tony Charman, Katarzyna Chawarska, Jana M. Iverson, Cheryl Klaiman, Rebecca J. Landa, Nicole McDonald, Daniel Messinger, Rebecca J. Schmidt, Carol L. Wilkinson, and Lonnie Zwaigenbaum, Pediatrics, July 16, 2024 (online) Address: Sally Ozonoff, MIND Institute and Department of Psychiatry and Behavioral Sciences, University of California Davis, 2825 50th St, Sacramento, CA 95817, [email protected].

—and—

“Large study confirms siblings of autistic children have 20% chance of autism,” news release, Marianne Russ Sharp, UC Davis, July 16, 2024.

—and—

“Mid-childhood autism sibling recurrence in infants with a family history of autism,” Tessel Bazelmans, Rowan Arthur, Greg Pasco, Elizabeth Shephard, Bosiljka Milosavljevic, Jannath Begum Ali, Andrew Pickles, Mark H. Johnson, Emily J. H. Jones, Tony Charman, and the BASIS/STAARS Team, Autism Research, July 8, 2024 (free online). Address: Tony Charman, Department of Psychology, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, De Crespigny Park, London, SE5 8AF, U.K., [email protected].