Muscle fibre type differentiation and satellite cell population in Werdnig-Hoffmann disease.

Quantitative analyses of the muscle fibre type distribution and satellite cell population were performed on biceps muscles from control infants 6-30 months of age and patients with Werdnig-Hoffmann (WH) disease aged 1-13 months. In muscles of control infants, type 1 fibres ranged from 34.5 to 52.5% of a total of 500 muscle fibres, similar to the percentage in adult muscle. The distribution of type 2A and 2B fibres varied slightly at different ages (type 2A, 19.3-42.8%; type 2B, 21.1-39.2%). Type 2C fibres ranged from 0.2 to 3.4% and did not tend to decrease with age up to 30 months. The ratio of satellite cells to total subsarcolemmal nuclei was 8.4 +/- 1.6% (5-21 months). In muscles in Werdnig-Hoffmann (WH) disease, undifferentiated type 2C fibres were significantly increased in number, ranging from 10.4 to 84.2% (P less than 0.005). The prevalence of the fibres was not necessarily proportional to the clinical severity, the onset of the disease, or the age at biopsy. Satellite cells in WH disease were significantly increased in number (14.4 +/- 3.1%) in comparison with control infants (P less than 0.005). The satellite cells in WH disease appeared quiescent without morphological characteristics of "activation".