Motoneuron death in normal and spinal muscular atrophy-affected human fetuses.

The onset and sequence of motoneuron death in the lumbar part of spinal cord of seven control and five affected fetuses carrying deletion of exon 7 in the SMN gene were studied by light and electron microscopy. Naturally occurring motoneuron death in control fetuses was detected between 8 and 13 weeks of gestation. In affected fetuses motoneuron death was prolonged and also observed at 16 and 20 weeks of gestation.