Genetic regulation of slowly progressing mild muscle atrophy in fast-twitch muscles of BUF/Mna rats.

BUF/Mna strain rats spontaneously develop slowly progressing mild-moderate muscle atrophy of extensor digitorum longus, tibialis, and extraocular muscles, which consist mainly of fast-twitch type fibers, at nearly 100% incidence. They have lighter extensor digitorum longus muscles than soleus muscles, when alive for more than 6 weeks. Genetic segregation of the development of the muscle atrophy was studied by crossing the BUF/ Mna strain with three other strains, ACI/NMs, WKY/NCrj, and BDIX, which were free of muscle atrophy. Two autosomal dominant susceptible genes, Mas-1 and Mas-2, determine the development of the muscle atrophy in these combinations of crosses.