INHERITED MUSCULAR DISORDER IN MUTANT JAPANESE-QUAIL (COTURNIX-COTURNIX-JAPONICA) - RELATIONSHIP BETWEEN THE DEVELOPMENT OF MUSCLE LESIONS AND AGE

The progression of the pathological changes that occur in the skeletal muscle was examined in 19 Japanese quail of the LWC strain, affected with an autosomal dominant inherited muscular disorder producing elect rical myotonia. The muscle samples were obtained every 10 days from 20 to 70 days of age. Muscle samples from 18 age-matched commercial quai l were used as normal controls. Characteristic histological lesions fo und in the skeletal muscles included sarcoplasmic masses, ringed fibre s, internal migration of nuclei and fibre size variation. These lesion s, which mainly occurred in the proximal muscles, appeared first in th e pectoral region and later in the muscles of the thoracic and pelvic limbs. The most predominant lesion observed at all ages consisted of s arcoplasmic masses. The presence of histological changes did not affec t muscle fibre typing by two staining methods, for myosin ATPase at pH 4.5, and by NADH-TR stain. The histological changes were observed in type 2A and less commonly in 2B fibres, but not in type 1. The pectora lis thoracicus muscle, in which lesions were particularly common, show ed abnormally large type 2B muscle fibres at 20 days of age. These fib res began to decrease in size at 30 days of age, and at 70 days had be come strikingly atrophic, their diameter being only about half that ob served at 20 days. The atrophic type 2B muscle fibres were eventually replaced by lipocytes. Chronological staging of the histopathological changes in muscle was impossible since no inter-relationship was obser ved between the age of the quail, the severity of clinical signs and t he extent of muscle lesions. This variability in the severity and age of onset may have been due to the variable expression or incomplete pe netrance of the defective gene. Because the disorder is hereditary and progressive in nature, it can be classified as a type of progressive muscular dystrophy. (C) 1995 Academic Press Limited