Acute infantile spinal muscular atrophy. Muscle apoptosis as a proposed pathogenetic mechanism.

Biopsy as well as autopsy studies of a child who died 8 weeks after birth from the acute infantile form of spinal muscular atrophy revealed classical morphological changes, including degeneration and loss of motoneurons in the spinal cord, loss of large myelinated fibres in anterior roots and neurogenic atrophy in muscle. New ultrastructural findings include massive muscle cell elimination by apoptosis with the formation of membrane-bound muscle cell fragments, apoptotic bodies. In addition, numerous immature muscle fibres were observed. The morphological findings raise the possibility that in a severely growth-retarded muscle, the process of muscle cell apoptosis removes the peripheral target of anterior horn cells resulting in secondary motoneuron death.