According to the American Journal of Human Genetics, it takes more mutations to trigger autism in women than in men, one study suggests. This could be a possible explanation as to why men are four times as likely to have the disorder, but does not explain why exactly women are remain “more protected.” Mutations that are inherited are also more likely to be passed on by the unaffected mother than from fathers.
These results suggest that women are generally resistant to mutations that contribute to autism. Researchers note the fact that autism is more difficult to diagnose in girls, which may mean that studies only enroll those girls who are severely affected and may therefore have more mutations.
The study uses data taken from the Simons Simplex Collection, which is a database of families that have one child with autism and unaffected parents and siblings. Evan Eichler, professor of genome sciences at the University of Washington in Seattle, and his colleagues took a sample of 109 girls and 653 boys with autism. They observed the number of copy number variants (CNVs) in each subject. CNVs are changes in the DNA of a person’s genome that results in abnormal cells. The larger the CNVm the more likely important genes and their functions will be disrupted.
The researchers found that females are twice as likely to carry very large CNVs (at least 400 kilobases long). When the analyzed CNVs associated with neurodevelopmental disorders, they found that females with autism are three times as likely as males to carry those specific CNVs.
Of the 27 of those in SSC group that were identified as having large CNVs, about 70% or 19 of them were inherited from the mother. Eichler says, “I think it’s really critical to identify these inherited components. We know they’re there, but we need to really focus on identifying the specific genes so we can advise [parents] a little more about recurrence.”
However the study still does not clarify whether this gender bias is in fact a result of genetics or just reflects differences in diagnosis and the way symptoms arise in females. It is also still unclear as to why women with autism transmit more mutations or how they are protected from autism. One thing is for certain; there is still ways to go in studying how females are affected differently by autism and what the reasons are behind this.
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