4/21/98
MILD FRIEDREICH'S ATAXIA ASSOCIATED WITH SMALL GENE DEFECTS IN NERVE TISSUE
Small genetic defects probably cause less severe disease than large ones in the neuromuscular disorder Friedreich's ataxia (FA), say MDA grantees at Baylor College of Medicine in Houston.
MDA grantees Pragna Patel and Sanjay Bidichandani were part of a research team that recently published an illustration of this likely principle as a "Case of the Month" in the March issue of Muscle & Nerve.
The researchers describe a 21-year-old woman with a genetic defect of the type known as a GAA triplet repeat in both chromosome 9 genes that code for a protein known as frataxin. A lack of the frataxin protein results in Friedreich's ataxia. While severe FA involves progressive loss of coordination, difficulty speaking and walking, heart problems and diabetes, the Baylor patient had only mild difficulty walking and keeping her balance.
A biopsy revealed small GAA triplet repeats in nerve tissue taken from her calf, while blood tests revealed significantly larger GAA triplet repeats in blood cells.
The authors, who also include Yadollah Harati and Hazem Machkas at Baylor, speculate that a small GAA repeat also exists in this patient's central nervous system, as in her calf nerve tissue, and that her disorder is relatively mild as a result.
The larger repeats in the blood cells apparently don't cause any problems but illustrate that genetic defects of this type aren't necessarily the same in all cells. In triplet repeat disorders, the size of the defect may change as the person grows and develops, and blood-cell DNA can't be relied upon in every patient for accurate genetic testing and prediction of disease course, as it usually can be in other types of genetic disorders.
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