Magazine article Science News

Let's Repeat: Mutation Gums Up Brain Cells

Magazine article Science News

Let's Repeat: Mutation Gums Up Brain Cells

Article excerpt

In most genetic disorders, the function of the gene that's mutated determines the symptoms of the disease. For the unusual kind of mutation that causes Huntington's disease and several similar brain disorders, however, the identity of the gene affected may not matter much.

That's the message emerging from studies of mutant mice created by Peter J. Detloff of the University of Alabama at Birmingham and his colleagues.

The researchers investigate disorders caused when a brief DNA sequence known as a CAG repeat occurs an abnormally large number of times in a gene's usual sequence. A half dozen or so neurodegenerative diseases stem from an excess of CAG repeats. Huntington's disease, for example, results when a certain gene harbors about 40 or more CAG repeats (SN: 6/10/95, p. 360).

Excess CAG repeats in a given gene add extra copies of the amino acid glutamine to the protein encoded by the gene. Detloff and other investigators have wondered whether almost any protein burdened with additional glutamines would cause a neurodegenerative disease or whether CAG repeats do their damage only in the context of specific genes.

The scientists engineered a strain of mice that has 146 extra CAG repeats in a gene that encodes hypoxanthine phosphoribosyltransferase (HPRT), an enzyme used by all cells. "You produce a full-length HPRT protein plus the added glutamines," says Detloff. The gene is active in brain cells, but the scientists had no reason to suspect that mutations in it would cause any problems. …

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