Comparing the markers to the pattern of disease in the families suggested the gene lies somewhere within a broad area of the chromosome that overlaps the area suggested by the 1994 study, Stine said. But that held true only in families where susceptibility to the disease appeared to be passed through the father, Stine said. This father's-side pattern for chromosome 18 has now also been found in the families that participated in the 1994 study, said Dr. Elliot Gershon, chief of the clinical neurogenetics branch of the federal mental health institute. Gershon said only a few known cases exist where a gene that can be inherited from both parents causes disease only when it comes from one. Stine said the explanation might be a process called imprinting, in which a gene functions if it came from one parent but is shut off if it came from the other parent.
People get two copies of most genes, one from each parent.
Stine, an assistant professor of psychiatry at the Johns Hopkins University School of Medicine in Baltimore, reports the result in the December issue of the American Journal of Human Genetics with Dr. J. Raymond DePaulo at Hopkins and other scientists. Dr. James Knowles, who studies manic-depression genetics at the Columbia University College of Physicians and Surgeons in New York, said the result adds to the evidence for a gene on chromosome 18. But he said the overall evidence is still too weak to consider it a confirmed finding. Chromosome 18 is one of three or four locations that look about equally promising for finding manic-depression genes, he said. Manic-depression, also called bipolar disorder, can combine episodes of depression with euphoria or irritability.