Researchers have long known that boys are nearly five times more likely than girls to be autistic, but the reason why has remained a mystery. American and French geneticists teaming up to study autism have now come up with new insight into why this disparity may exist between the genders in the occurrence of the disorder.
The massive study of DNA samples from 16,000 participants with neurodevelopmental disorders, and additional samples from 800 families with diagnosed cases of Autism Spectrum Disorder, reveals that it is not just that girls are less likely to be diagnosed as some have previously believed, but that the disorder does, in fact, occur less often in females than in males.
While conducting their research, the scientists discovered that genetic mutations likely to have caused the disorder were far more likely to have been passed on to children by the DNA of their mother than by that of their father. This was surprising, because fathers would, in theory, be much more likely to be affected by the disorder. They also found that female children were much more likely to have a greater number of the genetic mutations, and more severe genetic mutations, that are associated with neurodevelopmental disorders like autism, than males.
This information led the researchers to theorize that the greater occurrence of autism in males may be due to the fact that males are less able to adapt to genetic mutations than females and are thus more sensitive to the effects of such hits. Previous studies have linked as many as 500 different genes to autism, allowing for a lot of room for mutations to have an impact on development of the disorder.
The reason behind the potentially superior ability of females to adapt to genetic mutations is unknown. One explanation may be, however, that when a mutation occurs on an X chromosome, the female has another X chromosome from the other parent that allows for some compensation. It may simply “take more to push [females] into a state of intellectual disability.” This explanation may also help to explain why other neurodevelopmental disorders such as ADHD are also more prevalent among males.
One reason proposed for the passing on of existing genetic mutations associated with autism by the mother, rather than the father, is that fathers affected by autism may be less likely to form the types of social relationships that would result in creating children, whereas in women with the same type of genetic mutations, they may simply go unnoticed.
The researchers hope to expand their work to study even larger numbers of participants in hopes of being able to narrow down just which genetic mutations put children at the greatest risk for the development of autism and other neurodevelopmental disorders. Such a discovery could allow for more targeted treatments and therapies for those diagnosed. Understanding genetics may also help parents carrying genetic mutations to better understand their risks for having children with the disorder and to make informed decisions about having additional children.
Not all experts are convinced that studying genetics alone is the answer to providing insight into the mystery behind the gender disparities associated with autism. Other researchers are looking into such possibilities as the effects of exposure to sex hormones in utero as a key piece of the autism puzzle.
By Michele Wessel