Spinal muscular atrophy in childhood.

Diagnosis and classification of spinal muscular atrophy (SMA) in childhood are based on clinical, electrophysiological, and histological studies. The concept of maturational arrest of motoneurons and their targets (muscle cells in SMA type I) is documented by ultrastructural and immunohistochemical data. The prolongated or markedly delayed process of muscle cell and motoneuron elimination by apoptosis seen in SMA type I is discussed according to the new finding of a gene for a neuronal apoptosis inhibitory protein that is partially deleted in children with spinal muscular atrophy.