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Mutation revealed for adult Tay-Sachs.

Mutation revealed for adult Tay-Sachs

Scientists have discovered the genetic mutation responsible for the adult form of Tay-Sachs disease, a rare, degenerative brain disorder most commonly seen in its childhood form. The finding, along with the recent discovery of two mutations that can cause the childhood disorder, may allow screening of people who carry a Tay-Sachs gene to tell them which form of the disease they carry, says study coauthor Richard L. Proia, a biochemist at the National Institutes of Health.

People with late-onset Tay-Sachs suffer progressive mental and motor deterioration, with symptoms that vary from stuttering and falling to depression, schizophrenia and premature death. "But [adult Tay-Sachs] is nothing like infantile Tay-Sachs," which leads to death in early childhood, says biochemist Elizabeth F. Neufeld of the University of California, Los Angeles.

To contract either form of Tay-Sachs, a person must inherit a defective gene from both parents. The most common Tay-Sachs carriers, Ashkenazi Jews, frequently choose to take an enzyme test screening for this incurable disease and, if positive, usually opt for prenatal diagnosis or, in rare cases, not to conceive children. Genetic testing would be most useful in prenatal diagnosis, because the enzyme test may yield ambiguous results in fetuses predisposed to develop the adult form of the disease, says biochemist Eugene E. Grebner of Thomas Jefferson University in Philadelphia.

Both adult and infantile forms of the disease are caused by defects in an enzyme called beta-hexosaminidase. In the infantile disorder, brain cells do not produce this enzyme, and in the adult case, they produce a poorly functioning enzyme. In both, brain cells degenerate because they accumulate a membrane lipid normally metabolized by beta-hexosaminidase.

To find the adult mutation, Proia and geneticist Ruth Navon examined DNA from an adult Tay-Sachs patient who also carries the gene for infantile Tay-Sacs. The small amount of beta-hexosaminidase RNA his cells made from the late-onset mutant gene allowed the scientists to isolate the mutant. Sequencing the gene revealed the oddity: one changed base pair, a mutation for which eight additional adult Tay-Sachs patients proved positve and 20 asymptomatic individuals tested negative, the scientists report in the March 17 SCIENCE.

In separate work, Neufeld and Michael M. Kaback of the University of California, San Diego, found the same mutation. Their findings will appear next month in PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.
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Author:Wickelgren, Ingrid
Publication:Science News
Date:Mar 18, 1989
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