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X marks the spot.

X marks the spot

Evidence is mounting that, in some cases of manic depression,there is a gene near one tip of the X chromosome that predisposes its bearers to the disorder. Scientists who recently studied five families in Jerusalem used DNA-cutting enzymes to locate two genetic markers--one for color blindness, the other for a chemical deficiency that causes anemia--at the end of the long arm of the X chromosome. The markers occurred overwhelmingly among subjects with manic depression or related mood disorders (SN: 3/28/87, p.199).

Julien Mendlewicz of the Free University of Brussels,Belgium, and his colleagues now report that there is another manic depression marker in the same area of the X chromosome. DNA was isolated from 89 individuals, 41 of whom had manic depression or severe depression, in 10 families. A genetic marker for a blood coagulation factor located near the color blindness and anemia markers occurred mainly among family members with the psychiatric diagnoses.

The genetic link was emphasized by the fact that no fathersand sons shared mood disorders, say the researchers. The 23rd pair of human chromosomes consists of two X chromosomes for females and one X and one Y chromosome for males. The Y chromosome is inherited from the father.

There is probably more than one gene involved in predisposingpeople in different populations to manic depression, note the scientists in the May 30 LANCET. For instance, there is a genetic marker on chromosome 11 linked to manic depression among the Amish (SN: 2/28/87, p.132). But the investigators suggest that the long arm of the X chromosome may hold special promise for tracking down a predisposing gene.

"Banking of DNA samples from high-risk persons may lead tothe isolation and sequencing of the [X-chromosome] gene responsible for manic-depressive illness,' they say.
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Title Annotation:genetic aspects of manic depression
Publication:Science News
Date:Jun 13, 1987
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