Intrafamilial variability of X-linked progressive muscular dystrophy. Mild and acute form of X-linked muscular dystrophy in the same family.

Four of five afflicted boys in the family K. suffer from the Becker type of dystrophy and one from a more severe type. All affected boys and their mothers, who are three sisters, have undergone clinical, electromyographic, electrocardiographic and biochemical examination; muscle biopsy was performed in some boys. This family is a rare example of the intrafamilial variability of X-linked progressive muscular dystrophy. The possible explanation of the variability observed is discussed.