Baby Siblings at Risk

Autism recurs in families more often than previously thought; underscores importance of early

Many parents of children with autism want to know the likelihood of having another child on the spectrum. Knowing that younger siblings are at high risk can promote earlier screening, diagnosis and therapy, which may improve outcomes.

This year brought clearer guidance with the largest study of infants with one or more older siblings on the autism spectrum. It found that these younger siblings have close to a 1 in 5 chance (20 percent) of developing an autism spectrum disorder (ASD). This is considerably higher than previous estimates of 3 percent to 10 percent, based on much smaller studies that used various methods of ASD diagnosis. 

The researchers also found a higher rate of autism among baby brothers (about 1 in 4, or 25 percent) than among baby sisters (about 1 in 9, or 11 percent). For infants with more than one sibling on the autism spectrum, the risk of developing ASD was even higher—about 1 in 3.

The study, led by Sally Ozonoff, Ph.D., University of California, Davis, MIND Institute, assessed 664 infants, all of whom had at least one older sibling with a verified diagnosis of ASD. They did not find a link between autism risk and the severity of symptoms in the older sibling. Nor did they find an effect on risk from other family characteristics such as parental age or education, ethnicity or birth order, or an older sibling’s gender or IQ.

The researchers enrolled infants very early (two-thirds of them before 6 months) before symptoms of autism become obvious. The clinicians then followed the babies through 36 months of age. They used gold standard diagnostic methods and comprehensive assessments performed by expert clinicians. 

The findings highlight the need for close monitoring and screening of infants with an older sibling on the autism spectrum, Ozonoff says. Identifying early signs of autism can help clinicians and families take advantage of intervention strategies that can improve outcomes.

The study’s researchers are members of Autism Speaks Baby Siblings Research Consortium, an international network that coordinates studies and pools data from affected families in 21 sites in the US, Canada, Israel and the UK. Autism Speaks also funded the study’s cross-site analyses through a grant to co-author Gregory S. Young Ph.D., also of the University of California, Davis.


Ozonoff S, Young GS, Carter A, et al. Recurrence Risk for Autism Spectrum Disorders: A Baby Siblings Research Consortium StudyPediatrics. 2011; 128 (3) e488-95

 

Next: De Novo Genetic Changes Provide New Clues for Autism...

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