RECENT FINDINGS IN THE GENETICS OF BIPOLAR DISORDER, A report on a presentation 1 given by J. Raymond DePaulo, Jr., M.D., 2 Smooth Sailing, Spring 1996

In the attempt to locate a gene or genes for bipolar disorder, chromosome 18 has become a focus for researchers. A study implicating chromosome 18 by Dr. Wade Berrettini and his collaborators at Jefferson Medical School and the National Institute of Mental Health (NIMH) has attracted researchers to replicate his findings. Several research groups have had equivocal results with chromosome 18, most of which remain unpublished.

On the other hand, a newly published collaborative study by Colin Stine and a group of other investigators from Johns Hopkins, Stanford University, and the Cold Spring Harbor Laboratory not only supports the contention that a gene for bipolar disorder is located on chromosome 18, but also demonstrates a difference in the transmission of the illness from mothers versus fathers. Working with families in which several members have bipolar disorder, the Johns Hopkins group found no evidence of linkage to chromosome 18 in families with apparent maternal transmission and solid evidence of linkage to chromosome 18 in families with apparent paternal transmission.

This separation of families by "parent of origin" was suggested by an earlier article by Dr. Francis J. McMahon and colleagues, from the Johns Hopkins group. In the families they studied, maternal transmission was more common than paternal transmission, so Dr. McMahon encouraged researchers to look for a different mechanism of inheritance. Dr. Elliott Gershon and the collaborators from the NIMH/Jefferson study have now reevaluated the findings for the families in which linkage to chromosome 18 was first reported. They found more transmission through mothers than through fathers, and there was no evidence of linkage to chromosome 18 in the families with only maternal transmission.

This further analysis of data has substantially strengthened their statistical evidence for linkage to chromosome 18. Thus, we now have a confirmed report about the location of a gene for bipolar disorder. Although the evidence suggests that the gene (or genes) on chromosome 18 may be of major importance, its (or their) precise location still needs to be determined. Also, the parent-of-origin difference in transmission encourages additional study to find the mechanism of inheritance operating in most families affected by bipolar disorder, where transmission is predominantly or exclusively maternal.

These new findings are important because they establish that genetic studies in psychiatry are reproducible. Unfortunately for patients and family members, no blood test nor genetically inspired treatment for bipolar disorder is yet on the horizon. Further studies are needed to narrow the region of linkage so that gene isolation will be feasible.

Reference provided by Dr. DePaulo

Stine OC, Xu J, Koskela R, McMahon FJ, Gschwend M, Friddle C, Clark CD, McInnis MG, Simpson SG, Breschel TS, Vishio E, Riskin K, Feilotter H, Chen E, Shen S, Folstein S, Myers DA, Botstein D, Marr TG, DePaulo JR: Evidence for linkage of bipolar disorder to chromosome 18 with a parent-or-origin effect. Am J Hum Genet 57:1384-1394, 1995.

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1 Presented at a symposium March 9,1996

2 Professor of Psychiatry and Behavioral Sciences, and Director, Affective Disorders Clinic, Johns Hopkins University School Of Medicine.

by Anne Heasty, M.S.
Smooth Sailing: Spring 1996

For information about the Johns Hopkins genetic study of manic depression: www.med.jhu.edu/bipolar/

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