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Spontaneous Mutations Cause Majority of Autism Cases

Dominika Osmolska Psy.D.'s picture

A study out of the Cold Spring Harbor Laboratory led by Professor Michael Wigler suggests that many autism cases are caused by spontaneous genetic mutations across broad bands of the human genome. Specifically, the study estimates the minimum number of locations in the human genome - 250 to 300 - where gene copy number variation (CNV) can give rise to autism spectrum disorder (ASD). It also addresses the long observed gender bias of the disease, with boys being four times as likely to be diagnosed with the disease as girls.

Autism causes likely diverse

The specific causes of autism will likely be very diverse and the treatments available will be for a narrow subset of those affected. It appears that autism is a disorder with a very complex genetic basis and is unlikely to be precisely pinpointed.

Four years ago Wigler began publishing findings about the genetics of autism that surprised many in the field. He and his team of researchers noted the prevalence of what are called "de novo" genetic mutations in affected children – mutations that do not appear in either parent. This suggests a “spontaneous” and entirely novel mutation in the child. Mutations occur as extra copies of a section of the genome, or as missing pieces of the genome. In order for autism to manifest, it appears that several hundred of these “mistakes” must occur in combination. Some parental genetic input is likely in many of autism cases, which is what makes the subject so complex. While parents might carry small pieces of the autism puzzle and are not adversely affected by them, they might, in some cases, pass on just the right combination of genetic errors to their children. When these genetic mistakes undergo a further spontaneous mutation in the child, he or she becomes affected.

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Wigler’s study, however, suggests that up to fifty percent of autism cases are non-inherited, spontaneously occurring sets of mutations. These mutations must occur in a large biological network of genes strongly related to genes previously implicated in studies of autism and intellectual disability.

The study also shed light on the lower incidence of autism in girls. Females, it appears, carry a sort of built-in immunity to autism, and in order to be affected, they must incur much larger-scale gene mutation damage than boys - 15 genes per CNV on average for girls vs. only 2 for boys. This also helps explain why, when girls are affected by autism, the severity of their illness tends to be more profound.

The findings contribute invaluable research to the understanding of autism, a disorder that is becoming increasingly prevalent.

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