Mutagen hypersensitivity in Friedreich's ataxia

Cultured blood lymphocytes from nine patients with Friedreich's ataxia (FrA) and nine matched controls were exposed to a series of graded doses of mitomycin C and ethyl methane sulphonate and examined for the incidence of sister chromatid exchange (SCE). The spontaneous SCE levels did not differ between patients and controls, but the cells from each of the patients showed a significantly enhanced response to the induction of SCE by both mutagens - the patients' cells being up to 50% more sensitive than controls. Cultures from five FrA patients and five controls were analysed to determine the spontaneous incidence of chromosomal aberrations and exposed to a graded series of X-ray doses to measure their response to radiation-induced chromosome damage. The spontaneous aberration incidence in controls did not differ from that found in other control series, but the background incidence of aberrations in cells from the FrA patients was significantly above control levels and appeared to reflect an enhanced response to diagnostic exposure to radionuclides. The FrA cells showed a significantly enhanced in vitro response to chromosome aberration induction by X-rays, the net aberration yields being some 60% greater than those in irradiated controls at doses up to 200 rads. It is concluded that FrA is yet another syndrome which shows hypersensitivity to the induction of chromosome damage by mutagens. Possible factors responsible for this hypersensitivity are discussed and comparisons drawn with ataxia telangiectasia, another autosomal recessive disease characterized by enhanced X-ray sensitivity.