We studied a boy with severe infantile centronuclear myopathy (CNM) and his mother with clinical, electrophysiological, and pathological signs of skeletal muscle, peripheral nerve, and brain-stem disorder, and we believe that her condition represents a variation of her son's disease. His brother had similar symptoms and died at 4 days of age. The occurrence of this syndrome in a symptomatic mother and two severely affected sons suggests an autosomal dominant inheritance with variable expressivity. To our knowledge, this inheritance pattern has not been previously reported in severe (fatal) infantile CNM. The different courses in the mother and her offspring may be manifestations of a single or separate abnormal gene causing alteration of muscle and nerve maturation.