According to new research from the National Institutes of Health (NIH), a child who has a parent with a sibling on the spectrum is more likely to be diagnosed with autism spectrum disorder (ASD) compared to the general population. The study, published in Biological Psychiatry, analyzed health records of approximately 850,000 children born in Sweden between 2003-2012. Using the Swedish National Patient Register and the Multi-Generation Register, information on ASD diagnoses in both the child and parental generations were recorded.
Close to 13,000 Swedish children ended up with an autism diagnosis, about 1.5 percent of the cohort. However, children whose mother had one or more siblings with autism were three times more likely to have ASD than the general population and children whose fathers had one or more siblings on the spectrum were twice as likely to be diagnosed with autism than the general population. The study considered the slightly higher autism risk rate of children from mothers who had a sibling with ASD to that of the fathers to be insignificant. The research also reported that the autism risk rate was not different if the parent had a brother versus a sister with autism.
Ultimately, the researchers found that 3 to 5 percent of children whose parents have a sibling on the spectrum also have autism themselves. This points to a 100 to 230% increased chance of developing the disorder compared to the 1.5 percent autism rate in the general population. According to the authors, this is the first epidemiological study to provide an autism risk estimate for children with aunts or uncles on the spectrum.
Since autism was first identified, a strong male to female (4:1) bias has been recognized. This rate disparity has had many researchers consider if a female protective effect exists, the idea that females have a built-in resistance to the disorder for unknown reasons. The female protective effect theory further speculates that women could carry autism risk factors but remain unaffected. However, these women could transfer the risk to their sons who lack the same protective effect and therefore may later develop autism.
John Constantino, a co-author of the study, sheds light on this issue and says, “This finding challenges the existence of the a female protective effect, because if such an effect existed, the children of mothers with a sibling with ASD could be expected to have up to a 30% higher risk of ASD. Similarly, the researchers found no statistically significant increase in ASD risk for children whose uncles have ASD, compared to children whose aunts have the condition.” Read more at SafeMinds HERE.