Reasons Why Autism is Much More Common in Men Than Women

It has been known that males are at a greater risk for neurodevelopmental disorders, autism spectrum disorder being one of them. But the reasons as to why this was a prevalent statistic have been unclear--until now. 

The culprit may be a gene called RORA, otherwise known as related orphan receptor, and its role is believed to enhance the expression of hormone response elements. The presence of testosterone may negatively affect the roles of the RORA genes.

"Autism has a huge sex bias, and it's been proposed that higher levels of fetal testosterone may put a fetus at risk," said Valerie Hu, professor of biochemistry and molecular biology at George Washington University, according to Live Science. Ms. Hu is one of the researchers on a particular study to unearth the causes of a higher prevalence of autism in males.

Scientists believe that testosterone lowers the ability of cells to express the RORA gene, which increases the risk of autism. On the other hand, the estrogen hormone in females actually increases the ability of cells to express the RORA gene, which is why their diagnoses are much fewer.

Another explanation for ASD's greater risk in males can be found in a study conducted at the University Hospital of Lausanne in Switzerland. The researchers analyzed DNA samples of nearly 16,000 people with neurodevelopment disorders as well as 800 people with autism. They analyzed both copy-number variants (CNVs) and single-nucleotide variants (SNVs). CNVs are individual variations in the number of copies of a particular gene and SNVs are DNA sequence variations affecting a single nucleotide, according to Science Daily.

The results showed that females with ASD (or any other neurodevelopment disorder) had a greater number of harmful CNVs than did males with the same disorders, and the females also had a greater number of harmful SNVs in diagnoses of ASD. This implies that the female brain requires more extreme genetic alterations than their male counterparts, putting males at a greater risk for neurodevelopment disorders.

More details of the extensive research can be found in this Science Daily article as well as the published study in the American Journal of Human Genetics.