Variability in limb malformations and possible significance in the pathogenesis of an inherited congenital neuromuscular disease of Charolais cattle (syndrome of arthrogryposis and palatoschisis).

Limb abnormalities in 30 calves with an inherited congenital neuromuscular disorder known as syndrome of arthrogryposis and palatoschisis were classified according to the range of severity of joint deformity in either flexion or extension, and restricted joint movement. Joint movement was variably affected; it was either normal, lax, restricted in the range of mobility, or occasionally, fixed. The characteristic findings were: bilateral hyperextension of the hind fetlock, flexion deformity of the forelimb that particularly involved the fetlock and the carpus, with restricted articular movement and complete rigidity in some cases. One-third of calves also had medial deviation of the forelimb due to angular deformity of articular surfaces in the carpus. All nine live calves were floppy due to marked generalized muscular hypotonia. Birth weight of deformed calves was reduced. In some calves muscle development was impaired as judged by muscle weight, and histological examination. In some calves the gross appearance, muscle weight and histological examination revealed no abnormal development and indicated that the effects on skeletal muscle were secondary. No lesions were found in the spinal cord of 23 of 24 calves examined histologically. The remaining calf had a localized cavitation in the dorsal white matter at T2-3. Based on the observations in calves in this study it is proposed that both primary and secondary factors contribute to the phenotypic expression of this congenital deformity. The primary lesion is considered to be a neurogenic abnormality of differentiation in the central nervous system. Cytogenetic analysis of 16 carrier cows and two deformed calves showed normal karyotypes. Serology for Akabane virus in 16 carrier cows was negative.