A summary of the recent evidence, by Thomas Frazier, PhD and Stelios Georgiades, PhD.
Some family members of people with ASD often share many autism traits, but don’t have or show the number or severity of symptoms needed to be diagnosed. A recent study using the Interactive Autism Network looked at some features of autism in over 5500 individuals, some with multiple siblings with autism, some only one sibling. They wanted to determine if number of siblings with autism or sex of the sibling with autism influenced how these symptoms presented, if at all.
What did the researchers do?
When a family enrolls in the Interactive Autism Network not only do they enter in information about the person diagnosed with autism, they also fill out a form called the Social Responsiveness Scale on all family members. This is a quantitative measure of autism traits. Instead of saying autism: yes-or-no, the scale gives a number that corresponds to the presentation of features. It is used in people with autism, but has also been used to study features of autism of those without a diagnosis. Some people have higher levels than others but most people score around the middle. The higher the number, the more features of autism that person exhibits. In this study, the analysis consisted of 5515 brothers and sisters, 2858 with ASD and 2657 without ASD. They looked at how autism symptoms occur in male-only ASD-affected families vs. female-only affected families or in families with single vs. multiple cases of ASD. They also looked at the siblings of ASD children who did not have the condition but who had language delay or speech patterns usually seen in children with ASD. The sex of the siblings was also taken into account in the analysis.
What did the researchers find?
The research found that
- the non-ASD brothers and sisters (siblings) of children with ASD were more likely to show higher levels of symptoms if they were many members of their family with ASD,
- the non-ASD boys in these families were more likely to have a higher number of symptoms, as were boys with language delay or speech patterns usually seen in children with ASD,
- the children with ASD in families with several members with ASD had lower levels of symptoms than did the ASD children if they were the only child in the family with the condition, and
- the likelihood of having more than one child with ASD in a family was higher if that family had female members with ASD, and
- it is likely that girls need a much greater number of the genes related to ASD to produce the symptoms needed to warrant a diagnosis of ASD.
What does this mean?
Both the sex and the number of children with ASD in a family strongly influence the risk of their non-ASD siblings having a high number of autism symptoms. This again, links genetics to the causes of autism. These preliminary data suggest that siblings from certain families may have a higher likelihood of having children with ASD, but it is too early to base any family planning decisions on this data. It also emphasizes that girls have a higher genetic load, and that girls may be in some way, protected against some symptoms of autism.
Frazier TW, Youngstrom EA, Hardan AY, Georgiades S, Constantino JN, Eng C. (2015) Quantitative autism patterns recapitulate differential mechanisms of genetic transmission in single and multiple incidence families. Molecular Autism, 6:58. Full text here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4623917/