DNA fragmentation and BCL-2 expression in infantile spinal muscular atrophy.

Chromatin cleavage, a hallmark of apoptosis, was identified by in situ labeling in 55 +/- 7% of the muscle fibers in infantile spinal muscular atrophy (ISMA) and, to a lesser extent, in peripheral neuropathy indicating that DNA fragmentation is not specific to ISMA but a common feature in defect innervation. However, as DNA breaks are also known as a temporary process in differentiating myotubes DNA fragmentation may not always proceed to cell death. Therefore, it is currently not certain whether high rates of DNA fragmentation in ISMA are part of delayed muscle maturation due to neuronal defect or part of fibre breakdown. While atrophic muscle fibres in peripheral neuropathy displayed strong expression of bcl-2, a protein delaying onset of apoptosis, only 30% of the ISMA cases revealed weak bcl-2 expression assuming that immature muscle fibers are not able to produce a sufficient level of bcl-2.