Ozonoff, S., Young, G. S., Bradshaw, J., Charman, T., Chawarska, K., Iverson, J. M., Klaiman, C., Landa, R.J., McDonald, N., Messinger, D., Schmidt, R.J., Wilkinson, C.L., & Zwaigenbaum, L. (2024). Familial recurrence of autism: Updates from the Baby Siblings Research Consortium. Pediatrics, 154(2), https://doi.org/10.1542/peds.2023-065297
Reviewed by: Rachel Davis, EdM, LDT-C, BCBA, LBA-NJ and Robert H. LaRue, PhD, BCBA-D
Graduate School of Applied and Professional Psychology, Rutgers University
Why research this topic?
Families who already have one autistic child often want clear, research-based information about the likelihood that a later-born sibling may also be autistic. Ozonoff and colleagues (2011) reported the findings of the Baby Siblings Research Consortium (BSRC), which described the recurrence rates of autism spectrum disorder (ASD) of later-born children in families who had one child previously diagnosed with autism. In this study, the authors found that the recurrence rate of autism in later-born siblings was 18.7%, which is consistent with other population-based studies showing that siblings of autistic children have a 7-10 times greater likelihood of an autism diagnosis than children without an autistic sibling.
Because autism prevalence and diagnostic practices have changed significantly over the past decade, updated recurrence data were needed. Understanding recurrence risk helps guide family counseling, early development monitoring, and timely referral for evaluation for early intervention. The 2024 BSRC update provides the largest and most diverse infant sibling dataset to date.
What did the researchers do?
The researchers followed 1,605 infant siblings of autistic children across 18 international sites, tracking them from infancy through approximately age 3. Children between 35 and 60 months of age underwent standardized assessments, including the Autism Diagnostic Observation Schedule-2 (ADOS-2) and the Mullen Scales of Early Learning (MSEL). These assessments were administered by trained clinicians at outcome visits.
To calculate recurrence rates and identify factors predicting an autism diagnosis, the researchers used a statistical procedure referred to as hierarchical generalized linear modeling. This statistical model allowed the researchers to account for differences across the 18 study sites. This model adjusted for the site-level variability and allowed researchers to accurately evaluate how factors such as infant sex, number of autistic siblings, proband sex, race/ethnicity, and maternal education contributed to ASD outcome. This study’s prospective design, broad sample, and standardized assessment procedures strengthened the study and reduced biases that are typical of retrospective or clinical-referred samples.
What did the researchers find?
The study had several important key findings. The study revealed that 20.2% of later-born siblings were diagnosed with autism, which is comparable to the 18.7% recurrence rate reported in the 2011 study.
Recurrence varied across several child and family characteristics. Male infants had a higher recurrence (about 25% of later-born siblings) than female infants (about 13% of later-born siblings). They also found that infants with multiple affected siblings (multiplex families) had a higher recurrence rate (36.9%) than those with only one affected sibling (simplex families, 21.2%). The sex of the first autistic child (the proband) was also associated with the recurrence of autism. Families who had an autistic girl first had a recurrence rate of about 34.7%. Families who had an autistic boy first had a recurrence rate of about 22.5%. The authors also found that race impacted recurrence rates. The results indicate that white infants had a lower recurrence rate (17.4%) as compared to infants of other races (24.3%). Finally, the authors found that higher maternal education was associated with lower recurrence rates. Infants of mothers with a graduate degree had a recurrence rate of 16.9%. Conversely, infants of mothers with a high school education or less had a recurrence rate of 32.6%.
What are the strengths and limitations of the study?
This study benefits from being the largest and most diverse Baby and Sibling Research Consortium sample to date. The sample included 1605 infant siblings across 18 international sites. The researchers used standardized diagnostic assessments (ADOS and MSEL), ensuring consistency in diagnostic procedures. The study also incorporated advanced statistical modeling that accounted for differences across sites, which strengthened the reliability of the findings. The study also replicated the initial findings of the BSRC from 2011 and providing increased confidence in familial recurrence over time.
Despite the study’s strengths, some limitations are noted. The authors noted the potential for attrition bias. The participants who completed the study had higher developmental scores and maternal education levels than those who dropped out. However, the authors reported that this did not inflate recurrence estimates. The authors also noted that they included a limited range of sociodemographic variables (e.g., race, maternal education), which may not sufficiently explain all of the disparities in ASD diagnosis and recurrence rates. Another limiting factor was that the study was conducted while the diagnostic criteria for ASD were evolving, which could have impacted the findings. The authors also noted the potential for diagnostic bias in that autism diagnoses were made at around 36 months, which does not account for children who develop symptoms of autism later in childhood or adolescence.
What do the results mean?
The findings from the study indicate that familial recurrence of autism has remained stable, with about 1 in 5 later-born siblings diagnosed with autism. Male siblings, those from multiplex families, siblings of autistic girls, and children in families affected by socioeconomic disparities are more likely to develop an autism diagnosis. The results highlight the need for more screening and timely referral for diagnostic evaluation. For clinicians, educators, and families, the findings provide guidance for early monitoring, ensuring access to appropriate services and counseling to support informed decision-making during early childhood.
References
Ozonoff, S., Young, G. S., Carter, A., et al. (2011). Recurrence risk for autism spectrum disorders: a Baby Siblings Research Consortium study. Pediatrics,128(3). https://doi.org/10.1542/peds.2010-2825
Reference for this article:
Davis, R., & LaRue, R. H. (2026). Research synopsis: Familial recurrence of autism: Updates from the Baby Siblings Research Consortium. Science in Autism Treatment, 23(4).
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