INTELLIGENCE AND GENE FOR DUCHENNE MUSCULAR DYSTROPHY

Forty-seven DMD patients, their sibs, mothers, and some aunts and cousins were tested with standard intelligence tests: the WISC, WAIS, and Stanford Binet. The mean intelligence of DMD patients was found to fall approximately 1 SD below the population mean. About 30% of the patients are mentally defective, that is, have IQ's below 75, as compared to 9% of the normal population. Unlike the muscle disorder in these patients, the intellectual impairment is not progressive. The most likely explanation is that there is an early insult to the developing cerebrum, with no deterioration thereafter. The mental impairment is uniform; both the verbal and performance aspects of the IQ are equally impaired. There is no evidence that mental retardation is a secondary or environmental effect of the severe muscle disability. Mental impairment is found in the early stages of the disease as well as in the later ones. Differences in socio-economic class cannot explain the decrease. At both low and middle income brackets, the IQ's of dystrophics are significantly lower than those of their normal sibs. The degree of mental impairment in sporadic cases (with normal mothers) is not significantly different from that found in familial cases (with heterozygous mothers). The intellectual retardation in Duchenne patients appears to depend on the specific family genetic background; severe retardation is generally found in patients from dull families while normal intelligence is often found in patients from more intelligent families. The intelligence of females heterozygous for the DMD gene is not affected.