Expression of messenger RNA of the cardiac isoforms of troponin T and I inmyopathic skeletal muscle

In the absence of clinical signs, elevated values of the cardiac isoforms o f troponin T(cTnT) and I(cTnI) can be found in the serum samples of some pa tients with skeletal muscle myopathies; the cause is unclear: We studied th e messenger RNA (mRNA) expression of cTnT and cTnI in the skeletal muscles of 24 patients with histologically proven myopathies and in 18 patients in whom a myopathy could be excluded. For cTnT- and cTnI-mRNA determination, w e designed specific primer pairs for nested polymerase chain reaction. Afte r amplification, the products were digested with 2 restriction enzymes and visualized. We found cTnT mRNA in 7 skeletal muscle biopsy specimens (6 pat ients with Duchenne muscular dystrophy, 1 patient with a primary sarcoglyca nopathy) and cTnI mRNA in 6 (5 with Duchenne muscular dystrophy, 1 patient with a histologically negative biopsy). The mRNA of the cardiac isoforms, c TnT and cTnI, is expressed in the skeletal muscles of patients with Duchenn e muscular dystrophy, but also in some other myopathies. Further studies ar e needed to show whether the mRNA is translated into the protein, but serum levels of cTnT and cTnI in patients with Duchenne muscular dystrophy would seem indicate this.