Science / Medicine : Genetic Marker Helps Pinpoint Causes of Huntington’s

Researchers have identified a new genetic marker for Huntington’s disease that brings them one step closer to identification of the defective gene that causes the disease, a team of investigators has reported.

Discovery of the new marker sharply narrows the area of deoxyribonucleic acid (DNA) where researchers must search for the gene, reported the team, which is headed by geneticist James F. Gusella of Massachusetts General Hospital in Boston.

Researchers hope that identification of the defective gene, reported in the current issue of Science magazine, will lead to a therapy--or perhaps even a cure--for Huntington’s, which currently cannot be treated.

“But the more immediate consequence of the discovery is that it will increase the accuracy of diagnosing the disease in individuals who have a family history of the disease but no symptoms,” said neurologist Jack Penney of the University of Michigan, who is scientific director of the Huntington’s Disease Society of America.

Huntington’s disease strikes about one in every 20,000 Americans, with the onset normally between the ages of 35 and 45. Its cause is unknown, but the fatal disease kills so many cells at the center of the brain that a gaping hole is created. A child whose parent has the disease has a 50% chance of contracting it.

Researchers around the country have been using a genetic marker--a DNA fragment of characteristic length that is normally inherited along with the Huntington’s disease gene--called G8 to identify children and adults who have Huntington’s. But tests based on the use of the G8 marker are wrong about 5% of the time, and an incorrect diagnosis of Huntington’s can be devastating, said biochemist John J. Wasmuth of the University of California, Irvine, a co-author of the Science paper.

Several limited studies have shown that people who know they are at risk of Huntington’s have an abnormally high rate of depression and that 25% of those who are diagnosed with the disease attempt suicide. It is thus critically important that a diagnostic test for the disease have a high accuracy, Wasmuth said.

“As best we can tell with the new marker, the potential error rate is going to be considerably less than 4%,” he said.

At least three other groups of researchers in the United States and Great Britain have also identified new genetic markers for Huntington’s disease, although their results have not yet been published. The abundance of new markers, Penney said, makes researchers “confident” that they are close to locating the actual defective gene.

And when that gene is located, he said, “we will have a test that is 100% accurate, and we may be able to cure or prevent the disease.”