Spinal muscular atrophy: DNA fragmentation and immaturity of muscle fibers.

The presence of apoptotic fibers and the embryonic proteins desmin and vimentin were investigated in muscle biopsy specimens from patients with spinal muscular atrophy (SMA). Apoptosis was studied in 24 cases of SMA by means of in situ end labeling of nuclear DNA fragmentation using TUNEL staining and immunohistochemistry. Apoptotic nuclei were observed in 54.1% of the cases, and desmin and vimentin positive fibers were found in the majority of cases. A significant negative correlation was observed between the number of apoptotic nuclei and the duration of the disease, as well as between the number of desmin and vimentin positive fibers and the age of onset. These findings indicate that apoptosis, although probably a secondary phenomenon following denervation, plays a role in the progress of spinal muscular atrophy.