Benign neurogenic amyotrophy in Klinefelter's syndrome.

Two cases of benign neurogenic amyotrophy associated with Klinefelter's syndrome are reported. Both presented with slowly progressive, diffuse neurogenic muscle atrophy of juvenile onset. Both had a karyotype of XXY. Amplification, by the polymerase chain reaction, of a fragment of androgen receptor that was related to bulbospinal muscular atrophy, showed no abnormality. Treatment with androgen in one case provided no benefit. Benign neurogenic amyotrophy in the Klinefelter's syndrome is likely to be an independent type of motor neuron disease and suggests that the X chromosome plays an important part in the biology of motor neurons.