Anterior-horn cell degeneration and gross calf hypertrophy with adolescent onset. A new spinal muscular atrophy syndrome.

A new variant of spinal muscular atrophy (S.M.A.), characterised by adolescent onset, gross hypertrophy of calves, and a slowly progressive clinical course, was found in 5 patients, 3 of them in a series of 102 cases being studied in North-East England. Biopsy and electrophysiological studies indicated the presence of chronic progressive degeneration of anterior-horn cells.