Rare inherited variants in regions of non-coding DNA contribute to inherited cases of autism spectrum disorder (ASD), according to a new study by an international team led by scientists at University of California San Diego. The study is published in Science.
In recent years, researchers have firmly established that gene mutations appearing for the first time, called de novo mutations, contribute towards one-third of the cases of autism . The newly discovered risk factors differ from known genetic causes of autism in two important ways. First, these variants do not alter the genes directly but instead disrupt the neighboring DNA control elements that turn genes on and off, called cis-regulatory elements or CREs. Second, these variants do not occur as new mutations in children with autism, but instead are inherited from their parents.
"For ten years we've known that the genetic causes of autism consist partly of de novo mutations in the protein sequences of genes" said Jonathan Sebat, a professor of psychiatry, cellular and molecular medicine and pediatrics at UC San Diego School of Medicine and chief of the Beyster Center for Genomics of Psychiatric Genomics. "However, gene sequences represent only 2 percent of the genome."
The researchers then analyzed structural variants, deleted or duplicated segments of DNA that disrupt regulatory elements of genes, dubbed CRE-SVs. From the complete genomes of families, the researchers found that CRE-SVs that are inherited from parents also contributed to ASD.
"We also found that CRE-SVs were inherited predominantly from fathers, which was a surprise," said co-first author William M. Brandler, PhD, a postdoctoral scholar in Sebat's lab at UC San Diego and bioinformatics scientist at HLI.
"Previous studies have found evidence that some protein-coding variants are inherited predominantly from mothers, a phenomenon known as a maternal origin effect. The paternal origin effect we see for non-coding variants suggests that the inherited genetic contribution from mothers and fathers may be qualitatively different."
Sebat said current research does not explain with certainty what mechanism determines these parent-of-origin effects, but he has proposed a plausible model.
"There is a wide spectrum of genetic variation in the human population, with coding variants having strong effects and noncoding variants having weaker effects", he said. "If men and women differ in their capacity to tolerate such variants, this could give rise to the parent-of-origin effects that we see."