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Manic depression: suspect gene acquitted.

Manic depression: Suspect gene acquitted

A 1987 study of manic-depressive illness among six generations of an Amish family showed strong evidence that a single gene -- its presence inferred from two "marker" gene --carried the disorder. Further study of the family now casts serious doubt on that particular link, while leaving open the possibility that manic depression has some yet-unindentified genetic basis.

The 1987 study analyzed the correlation between manic depression, also known as bipolar affective disorder, and two genes on chromosome 11 (SN: 2/28/87, p.132). Researchers found that family members with manic depression were likely to have particular forms of an insulin gene and of a gene associated with benign tumors. Neither of these marker genes appeared to cause manic depression, but the correlation suggested that a gene involved in manic depression lay near them on the same chromosome.

The new study, reported in the Nov. 16 NATURE, adds 39 people from five generations to the original 81-member pedigree. It also incorporates new data on some family members studied earlier. Since the original study, one participant has become manic-depressive and another has developed major depressive disorder. In 10 other original subjects, investigations had analyzed only one of the two marker genes.

When the researchers took these factors into account in reexamining the link between manic depression of the two marker genes, they found that the likelihood of a single gene on chromosome 11 carrying the disorder in this family dropped u,000-fold, says study leader Steven M. Paul of the National Institute of Mental Health in Bethesda, Md. Although the updated study does not absolutely rule out this possibility, it makes it so unlikely as to be "unpublishable," paul says.

The revised pedigrees still indicate manic depression has some sort of genetic basis, he syas. It may involve more than one gene or a single gene on another chromosome, he suggests.

The Old Amish, members of a religious sect in Pennsylvania, number approximatley 15,000 in large, well--documented families descended from 30 pioneer couples. Consequently scientists view then as ideal subjects for genetic studies. And because very few Amish abuse alhohol or drugs, researchers cna study their mental illness without these confounding factors.
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Author:McKenzie, A.
Publication:Science News
Date:Nov 18, 1989
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