Depression in the family.

Many complex disorders, such as manic depressive illness, often run in families but do not show the simple, fixed patterns of inheritance observed in diseases caused by a single defective gene. Will the new applications of molecular biology, such as those being used to locate the gene associated with Huntington's disease (SN: 12/24&31/83, p. 408), be applicable to disorders with more complicated genetics? Kenneth K. Kidd of Yale University School of Medicine now reports the "first strongly positive" finding in the molecular genetics of depression.

Kidd has examined the DNA of members of an Old Order Amish family studied by Janice A. Egeland of Miami University (North Office) in Hershey, Pa. Of 51 family members, 11 have an affective disorder, either manic depressive illness or major depression. Genetically, the disease in this family is associated with a single position near the tip of the short arm of chromosome 11, near the gene for insulin, according to preliminary data of research by Kidd and Daniela Gerhard and David Housman of the Massachusetts Institute of Technology. The presence of a specific marker (a restriction-fragment-linked polymorphism, or RFLP) on the short arm of chromosome 11 increases 100-fold the likelihood of affective disease in a member of this family, Kidd reports. But the gene on chromosome 11 is only part of the picture. It appears to be required, but is not sufficient, for the disease to occur -- only half the family members who appear to carry the gene show symptoms of depression. This type of research is expected to clarify the heterogeneity of affective disorders and lead to better diagnosis and treatment. An international effort is now under way to identify more large families with members affected with manic depressive illness.