IMMUNOHISTOCHEMICAL ANALYSIS OF THE DISTRIBUTION OF MYOD1 IN MUSCLE BIOPSIES OF PRIMARY MYOPATHIES AND NEUROGENIC ATROPHY

The expression of the myogenic determination gene MyoD1 plays a primar y role in the commitment of primitive mesenchymal cells to a striated muscle lineage and is down-regulated during later stages of differenti ation. To determine the potential role of this gene in myopathic condi tions, we examined its expression by means of immunohistochemical anal ysis, using a series of muscle biopsies from 14 patients with a variet y of primary myopathies and neurogenic disorders. Utilizing the avidin -biotin-complex technique, cryostat sections were stained with monoclo nal antibody 5.8 A, which we have previously described as having a hig h level of specificity for tumors with rhabdomyoblastic differentiatio n. Of special interest was the observation in 4 of 8 cases of neurogen ic atrophy of varying levels of cytoplasmic positivity of muscle fiber s, appearing to correlate with their degree of atrophy, in addition to weak nuclear staining. Muscle biopsies from 2 patients with Duchenne' s muscular dystrophy and 2 patients with autoimmune inflammatory myopa thies demonstrated various levels of nuclear positivity in scattered f oci that appeared to correlate with areas of regeneration. A biopsy fr om a single case of neurogenic atrophy secondary to infantile spinal m uscular atrophy (Werdnig-Hoffmann's disease) demonstrated diffuse but relatively weak staining of myofiber nuclei, in contrast to sections o f normal striated muscle and muscle biopsies from patients with unexpl ained myoglobinuria, which exhibited only minimal amounts of staining. These data are compatible with observations that MyoD1 expression is related to electrical activity and muscle regeneration.