[MIM*253300] the early infantile form, characterized by profound muscle weakness and wasting with onset at or shortly after birth; death occurs usually before 2 years of age. Autosomal recessive inheritance, caused by mutation in the survival motor neuron gene (SMN1) on 5q. About half of affected patients are also missing both homologues of a neighboring gene that encodes neuronal apoptosis inhibitory protein (NAIP), the loss of which is thought to influence the severity of the disease. SYN: familial spinal muscular atrophy, Hoffmann muscular atrophy, infantile muscular atrophy, infantile progressive spinal muscular atrophy, progressive infantile spinal muscular atrophy, Werdnig-Hoffmann disease, Werdnig-Hoffmann muscular atrophy.