Boston, MA -- An international team of 53 researchers hasoffered the most convincing evidence so far linking bipolar disorder,also known as manic depression, to two chromosomal regions in the humangenome. The finding gives scientists refined targets for further genestudies.
"Even though bipolar disorder affects millions of peoplearound the world-sometimes throughout their lifetimes-what weunderstand to be biologically relevant at the genetic level is notterribly characterized," said Matthew McQueen, lead author andpostdoctoral fellow in the Department of Epidemiology at the HarvardSchool of Public Health (HSPH). "This research can help focus the fieldto identify viable candidate genes."
The study will appear in theOctober issue of the American Journal of Human Genetics and isavailable now in the journal's electronic edition online at http://www.journals.uchicago.edu/AJHG/journal/contents/v77n4.html.
Morethan two million American adults have bipolar disorder, according tothe National Institute of Mental Health. Patients typically experiencedramatic mood swings from episodes of euphoria and high energy tofeelings of intense sadness, fatigue, and even suicide. Psychiatristshave identified two primary forms of the illness: bipolar I disorder,which is the classic form of recurring mania and depression, andbipolar II disorder, which has less severe episodes of mania. Treatmentoften includes medication.
The exact cause of the illness remainsunknown, but scientists suspect the involvement of several genes,coupled with environmental influences. A number of individual studieshave suggested genomic regions linked to bipolar disorder, but theirresults have been inconsistent and difficult to replicate, leaving thefield "standing at a crossroads, wondering in which direction to gonext," said McQueen.
To establish more definitive research,McQueen and his colleagues did something unusual. They secured and thencombined original genome scan data from 11 independent linkage studies,instead of relying on the more common approach of using summary datafrom such studies.
"The use of original data made a significantdifference in our ability to control for variation in several factorsamong the different data sets and to make the overall analysis muchmore consistent and powerful," said Nan Laird, HSPH Professor ofBiostatistics and senior author on the paper.
The resultinganalysis involved 1,067 families and 5,179 individuals from NorthAmerica, Italy, Germany, Portugal, the UK, Ireland, and Israel, who hadprovided blood samples and family medical histories. The research teamcombined the data into a single genome scan and found strong geneticsignals on chromosomes 6 and 8. The team now hopes to narrow the searchto find associations between specific genes and the mental illness.
Theanalysis was funded through the Study of Genetic Determinants ofBipolar Disorder Project at the National Institute of Mental Health.Other researchers on the analysis team represented MassachusettsGeneral Hospital, The Broad Institute, and the University of Pittsburgh.
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