September 06, 2016
1 min read

Children with affected older sibling at 14-fold increased risk for ASD

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Darios Getahun

Younger siblings of children diagnosed with an autism spectrum disorder were at increased risk for affectation also, according to recent study findings.

“Studies that examine genetic influences on [autism spectrum disorders (ASD)] show a higher concordance of ASD in monozygotic twins than in dizygotic twins and a much higher risk of ASD in siblings of an affected child than in the background population,” Darios Getahun, MD, PhD, of the department of research and evaluation at Kaiser Permanente Southern California, and colleagues wrote. “A recent Danish study showed that younger siblings with an ASD afflicted older sibling have a nearly sevenfold increased risk of ASD than those with an unaffected older sibling. This finding is based on a homogeneous white population.”

To assess the risks of ASD in younger siblings of affected older siblings and if the risks are magnified by sex, race and ethnicity or gestational age at birth, Getahun and colleagues included Kaiser Permanente members in Southern California who had at least two children born at 28 to 42 weeks’ gestation to the same mother within a 10-year period. The researchers examined 53,336 children aged 2 to 11 years, of which 1.11% were diagnosed with ASD. Children’s races and ethnicities were categorized as non-Hispanic white, non-Hispanic black, Hispanic, non-Hispanic Asian/Pacific Islander or other.

Analysis showed that ASD rates were 0.92% for younger siblings of unaffected children vs. 11.3% for younger siblings of affected older children (adjusted RR = 14.27; 95% CI, 11.41-17.83). ASD risk in younger brothers of affected siblings, regardless of their sex status, was almost three times greater (aRR = 2.93; 95% CI, 1.88-4.57) compared with younger sisters. In addition, race, ethnicity and gestational age were associated with similar risk across all groups.

“It’s possible that parents who have an older child with an autism diagnosis are more likely to have their younger siblings tested, too, resulting in a higher rate of diagnoses among younger siblings, compared with parents who do not have children diagnosed with an autism spectrum disorder,” Getahun said in a press release. – by Kate Sherrer

Disclosure: The researchers report no relevant financial disclosures.