Review of spinal muscular atrophy (SMA) in brown Swiss cattle.

Abstract

Spinal muscular atrophy (SMA) is a heritable condition in Brown Swiss cattle characterized by profound muscular atrophy affecting appendicular muscles, particularly of the rear limb. Axial muscles are also affected. The affected ventral horn neurons are initially swollen and chromatolytic; this is followed by a shrunken appearance, necrosis, and neuronophagia. It is not uncommon to see “empty beds” that are ghosts of previous perikarya. There is an obvious gliosis with the presence of glial nodules. A total of 53 SMA cases were either reported to us or received and studied by the Congenital Defects Laboratory at Kansas State University. All calves underwent a thorough clinical examination. They were then euthanatized using T-61 and immediately underwent a standardized necropsy procedure. Brains were obtained by removal of the dorsal cranium, and spinal cords were removed by removal of the dorsal vertebral arches. Muscle samples were taken and attached by stapling to tongue depressors for identification. Peripheral nerves were sampled also. Tissues were processed for light and electron microscopy studies. Iowa was the geographic origin of 10 of the cases, followed by Wisconsin and Texas with 5 cases each. The mean age of onset was 3.1 weeks with a standard deviation of 1.88. There were 5 calves that were affected at birth. The oldest reported age in this group was 8 weeks. The mean duration of recumbency before death was 6.4 weeks, with a maximum of 12 weeks in 2 of them. The affected cases were sired by 21 bulls, with 1 sire, #4, accounting for 9 of them. Spinal muscular atrophy can be confused with several other diseases, most notably nutritional myopathy. With the latter condition, however, alpha motor neurons are not involved, and hyaline degeneration is prominent in muscle tissue. Spinal muscular atrophy (SMA) is a neurodegenerative disease of Brown Swiss cattle that is inherited as