Benign Familial Spinal Muscular Atrophy With Hypertrophy of the Calves

• A father and son had benign spinal muscular atrophy syndrome, clinically characterized only by cramps and gross hypertrophy of the calves. The electromyogram and biopsy specimen indicated a motor neuron disease in both patients. In the son, "pseudomyopathic" changes were also observed. To our knowledge, similar cases of benign spinal muscular atrophy with hypertrophy of the calves and probable autosomal dominant inheritance have not been previously described.