Scientists at the University of Montreal have discovered what they believe causes a genetic susceptibility toward autism — and on a note possibly related only to gene mutation, can cause a significant drop in a person's intelligence quotient (IQ) by as much as 25 points.
The drop is caused by the absence of a gene copy — gene 16, which the scientists were researching in tandem with the frequency of spectrum predisposal, and noticed that mutations in the gene also usually indicated an effect on IQ. The mutation? A missing copy of the gene.
"[A] missing copy of a region in chromosome 16 results in a 25-point [IQ] drop in carriers. Addition of a copy in the same genomic region results in an approximate 16-point drop," said Sébastien Jacquemont, a clinical researcher at CHU Sainte-Justine affiliated with the University of Montreal. "Strangely enough, even if carriers show much differentiated sets of symptoms — and sometimes no symptoms at all — the specific effect of these two mutations seems to remain the same."
To collect data, Jacquemont, in collaboration with other international researchers, surveyed 700 families that had one or more relatives with a mutation in gene 16, finding that even participants with a normal IQ still had a significant drop.
"Intellectual faculties are the sum of many factors, the majority of which are genetic and inherited from parents. Each first-degree relative — parents and offspring, siblings — has 50 percent of their genetic code in common and therefore 50 percent of the genetic factors that partially determine cognition," explained Jacquemont. For example, depending on the additional factors involved, a 25-point IQ drop can determine whether or not a person has crossed the threshold of 'intellectual disability.'"
While the results of the study are promising in terms of leading scientists toward ways in which we can understand — and even one day prevent — autism, further studies will need to be conducted to make a definitive call on the exact nature of the gene.
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