September 27, 2017
2 min read

Autism risk associated with gender of older sibling

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Female children diagnosed with autism spectrum disorder are more likely to have younger siblings also diagnosed with the disorder, with higher rates observed in younger male siblings regardless of the older sibling’s sex, according to a study published in JAMA Pediatrics.

“Because the cause of most cases of ASD cannot yet be explained using genetic approaches, several groups have sought to associate environmental exposures with ASD. However, the risk conferred by genomic variation in combination with environmental exposures remains unknown,” Nathan Palmer, PhD, from the department of biomedical informatics at Harvard Medical School, and colleagues wrote.

“Understanding the rate at which ASD diagnoses are shared among siblings in a family will aid in the interpretation of the genetic and environmental factors that increase the familial risk for ASD, leading to improved screening and counseling at point of care,” the researchers continued.

To evaluate recurrence rates of ASD among siblings with specific emphasis on the siblings’ sex, the researchers conducted an observational study that analyzed data regarding 1,583,271 families participating in commercial health care insurance plans. Of these families, 37,507 had at least one ASD diagnosis. All participants were enrolled in health insurance between Jan. 1, 2008, and Feb. 29, 2016, and pairs of siblings between the ages of 4 and 18 were observed for a minimum of 12 months.

Of the children included (n = 3,166,542), 1,547,266 were female and 1,619,174 were male (SD age, 11.2 [4.7] years). The prevalence rate of ASD was observed at 1.96% for boys (95% CI, 1.94%-1.98%) and 0.50% for girls (95% CI, 0.49%-0.51%). When the older sibling diagnosed with ASD was male, 4.2% of female siblings (95% CI, 3.8%-4.7%) and 12.9% of male siblings (95% CI, 12.2%-13.6%) were also diagnosed. For older female siblings diagnosed with ASD, 7.6% of younger female siblings (95% CI, 6.5%-8.9%) and 16.7% of male siblings (95% CI, 15.2%-18.4%) were also diagnosed.

“The sample size of our study enabled a high-confidence analysis of sex-specific ASD rates of recurrence in the general population, which prior studies were underpowered to detect,” Palmer and colleagues wrote. “These findings could be incorporated into screening and counseling for families with no etiologic factors.” – by Katherine Bortz

Disclosure: The authors report no relevant financial disclosures.