New studies show that autism may be a disorder of synapses, depicted here… (David Grubin Productions )
Autism spectrum disorders can be caused by as many as 300 or so rare genetic mutations, scientists reported Wednesday. The research strongly implicates genetics, including spontaneous gene mutations, in the development of the disorder.
But why do four times as many males as females develop autism spectrum disorder? In one of the three papers published in the journal Neuron, researchers suggest that girls are more resistant to gene mutations than boys. Girls seem to require a higher number of gene mutations to become afflicted with autism spectrum disorder.
But it's also possible that a genetic mutation in a boy that causes autism spectrum disorder may produce a different kind of neurological or behavioral problem later in life, such as anorexia nervosa, which affects about 10 times more girls than boys, said Michael Ronemus, a co-author on two of the papers and a research investigator at Cold Spring Harbor Laboratory in Cold Spring Harbor, N.Y.
"The question is: What is the fate of female carriers?" Ronemus said. "Do they remain asymptomatic or is there another disorder that has neurological or behavioral components that shows the opposite gender bias?"
It's hard to imagine that the gene mutations that cause autism in boys don't have some effect on girls eventually, he said. And, there are many examples of gene mutations that don't cause disease until a particular time of life.
However, there is no proof as of yet that the same mutations cause different disorders in males and females. "We give as an example anorexia nervosa. We don't have any evidence for that," Ronemus said. "It's speculation."
Other theories to explain why more males are affected include the idea that because female brains develop faster than male brains early in life, there could be a strength to the female brain that is protective of autism. Another study published earlier this year proposed that hormonal differences influence gene expression, leading to a higher incidence in males.
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