Skeletal muscle pathology in ovine congenital progressive muscular dystrophy. 2. Myofiber morphometry.

Fiber-type proportions were determined in 12 skeletal muscles (peronaeus tertius, tibialis cranialis, tensor fascia lata, psoas major, extensor digitorum lateralis, tensor fascia antibrachii, vastus intermedius, soleus, anconaeus, and flexor digitorum superficialis of fore and hind limb) from infantile (20 weeks), juvenile (16 months) and adult (2.5 and 3.5 years) Merino sheep with ovine congenital progressive muscular dystrophy and in age-matched controls. Although confined to type I fibers, lesions were severe not only in type I fiber dominant muscles (vastus intermedius, soleus and anconaeus) but also in the type II dominant medial triceps brachii and in the superficial digital flexors which had approximately equal proportions of both fiber types. The frequency distribution curves of myofiber diameter in dystrophic anconaeus and superficial digital flexor of the fore limb altered as the disease progressed. In young sheep (20 weeks) type I fibers increased in size, then in juvenile and adult sheep the curves became flatter and broader and lost symmetry due to the presence of hypertrophic and atrophic fibers. The fiber diameter profiles were similar to those seen in Duchenne dystrophy in humans.