Previous studies of twins and adopted siblings have suggested there likely are genes in common underlying alcoholism and depression, and that the two disorders seem to run in families. But the lead researcher of the new study says this is the first report of a specific gene that seems to increase risk for both disorders.
"Clinicians have observed a connection between these two disorders for years, so we are excited to have found what could be a molecular underpinning for that association," said Alison Goate, the Washington University School of Medicine researcher who led the study.
Follow-up research might help reveal the underlying biology that makes some people susceptible to alcoholism, others to depression, some to both diseases, and others to neither. Goate says a variation or alteration of the CHRM2 gene influences those four separate conditions.
The study is published in the September issue of the journal Human Molecular Genetics.
"What you want is to see someone obtain the same results in an independent study," said Goate, a psychiatric geneticist.
Goate said the researchers will know in a few weeks whether they can replicate the finding from another group of people they're studying.
Peter McGuffin, a psychiatric geneticist at the Institute of Psychiatry at King's College in London, said that if Goate's finding holds and is replicated by others, it will provide another potential target for developing new drugs to treat depression and alcoholism.
McGuffin, who said he is working "feverishly" on the genetics of depression, said it is the first time this particular gene has been implicated. He said probably multiple genes are involved in these two disorders.
Goate's team analyzed DNA from 2,310 people from 262 families in which at least three members were alcoholic. Some individuals in these families were also depressed alcoholics. Both groups had similar distinguishing characteristics in their DNA in a region on chromosome 7. Participants with both maladies were most likely to have the genetic similarity.
Within that region of the chromosome, researchers isolated the CHRM2 gene, which is involved in attention, learning, memory and cognition. Goate's team found the gene was strongly associated with both alcoholism and depression. The association was strongest in those with both disorders, suggesting it's a susceptibility gene that puts people at risk for developing both diseases.