Autism affects people in so many different ways and to such varying degrees that it's hard to diagnose. It's harder still to discern its cause. Scientists have known that environmental and genetic factors come into play, but the complexity of both influences has made them virtually impenetrable. Now, however, researchers at Duke University's Center for Human Genetics have found a new way to look at how genes contribute to the disease. And that insight, which they present today at a meeting of the American Society for Human Genetics, might just simplify the task of unraveling autism's origins.
The clue, explains senior researcher Margaret Pericak-Vance, is that a phenomenon known as genomic imprinting may be at work in passing on autism. In short, imprinting is a process by which a gene's expression in a child depends on which parent donated it before development. Unlike Mendelian genetics, in which dominant and recessive genes control the results, imprinting is a kind of molecular battle of the sexes; by silencing the other parent's copy of a gene, a mother or father advances their own genetic interests. And although initially discovered in insects, genomic imprinting has recently been found in some rare human disorders, such as Prader-Willi and Angelman syndromesboth of which can produce symptoms like those in autism.
"Many children with these syndromes have altered genes in the same region of chromosome 15 that we are looking at in autism," Pericak-Vance said. So they were looking as well at a region on chromosome 7 implicated in autism, which also contained imprinting genes. To test their idea that imprinting was involved by way of these chromosomes, Pericak-Vance and colleagues examined 82 families who had at least two members affected by autism in some form. Their findings suggested a paternal effect on chromosome 7 and a maternal effect on chromosome 15. "Once we better understand the genetic factors involved in autism, genetic testing can theoretically be offered to families at risk," notes postdoctoral fellow Allison Ashley-Koch. "In addition, identification of such genes will pave the way for development of therapies to improve the quality of life for these children."