Nebulin expression in patients with nemaline myopathy

Nemaline myopathy is a structural congenital myopathy which may show both a utosomal dominant and autosomal recessive inheritance patterns. Mutations i n three different genes have been identified as the cause of nemaline myopa thy: the gene for slow alpha -tropomyosin 3 (TPM3) at 1q22-23, the nebulin gene (NEB) at 2q21.1-q22, and the actin gene (ACTA1) at 1q42. The typical a utosomal recessive form appears to be the most common one and is caused by mutations in the nebulin gene. We have studied the pattern of nebulin label ing, in patients with the typical congenital form (ten patients), the sever e congenital form (two patients) or the mild, childhood-onset form tone pat ient), using antibodies against three different domains of nebulin. A quali tative and quantitative nebulin analysis in muscle tissue showed the presen ce of nebulin in myofibers from all patients. Some differences relating to the rod structure were observed. The majority of the lar est subsarcolemmal rods were not labeled with the N2 nebulin antibody (I-band epitope) and sh owed an indistinct pattern with the two antibodies directed to the Z-band p ortion of nebulin (epitopes M176-181 and serine-rich domain). Diffuse rods were not revealed using the three antibodies. A discordant pattern of nebul in N2 epitope labeling was found in two affected sisters with a mutation in the nebulin gene, suggesting that modifications in nebulin distribution in side the rods might occur with the progression of the disease. Western blot analysis showed no direct correlation with immunofluorescence data. In nin e patients, the band had a molecular weight comparable to the normal contro l, while in one patient, it was detected with a higher molecular weight. Ou r results suggest that presence/absence of specific nebulin Z-band epitopes in rod structures is variable and could depend on the degree of rod organi zation. (C) 2001 Elsevier Science B.V. All rights reserved.