A couple of reports in Science News this week pick up on stories we have been following. The first is a “backgrounder” on hyeractivity and food additives; the second illuminates one of the murky patterns of genetic transmission, heredibility of gene variants in ADHD and autistic spectrum not seen in other psychiatric disorders.
The second report moves our knowledge of the genetics of ADHD and Autism Spectrum disorders another step of depth (See blogs of June 12 ’11 and November 21 ’10). Tina Hesman Saey discusses the issue of “copy variants”, when duplicate or missing copies of certain genes correlate with clinical conditions. I will quote a portion of her article:
Up to 75 percent of people with autism spectrum disorders also have symptoms of ADHD, but researchers did not know if the genetic causes were the same as in people who have ADHD alone. Previous research has shown that people with autism or schizophrenia often have genes that are missing or duplicated more often than normal. Such added or subtracted genes are known as copy number variants. Healthy people may have extra copies of several genes or lack some entirely, but missing or doubling up on certain genes can lead to disease.
Unlike people with schizophrenia or autism, people with ADHD are no more likely than average to have missing or copied genes, the researchers report in the Aug. 10 Science Translational Medicine. But about 8 percent of people with ADHD have rare copy number variants that may cause or contribute to the disorder. A subset of those genes are perturbed both in people with ADHD and in people with autism spectrum disorders, indicating that the disorders may have some common genetic causes.
An examination of DNA from parents of 173 of the children in the new study showed that copy number variants associated with ADHD are often inherited from a parent who also often has the disorder. That differs from autism and schizophrenia, where the genes associated with the condition are often newly deleted or duplicated in the child with the disorder, not passed down from parents.
More copy number variants and other types of genetic changes remain to be uncovered, scientists say. Many different brain processes are probably involved in the disorders, and disrupting any of them could produce similar outcomes, Elia says. “We may end up having thousands of variants and not just a handful,” she says.