Insulin-like growth factor-I levels and gene expression in ovine hereditary chondrodysplasia (Spider Lamb Syndrome)

Hereditary Chondrodysplasia or Spider Lamb Syndrome (SLS) is an inherited, semi-lethal, musculo-skeletal disease affecting lambs primarily of Suffolk or Hampshire breeding. Deformities of the limbs and spinal column along with multiple sites of ossification at the anconeal process are diagnostic for the disease. Muscle atrophy is also predominant. We have investigated the relationship between SLS and circulating levels of IGF-I and the IGF-BPs in older (50-80 d of age) animals. Serum IGF-I levels were lower (P<0.01) in SLS affected lambs (117 ng/ml) than in phenotypically normal lambs (188 ng/ml) while serum levels of the 32 kDa BP increased (P<0.01) 77% in SLS affected lambs as compared to contemporary controls. All other IGF-BPs appeared to be unaffected in this group. Gene expression of IGF-I and -II in the liver and muscle of younger (16-22 d of age) lambs was also measured. There were no differences in IGF-II expression in either muscle or liver between SLS affected and phenotypically normal control lambs. Muscle IGF-I expression also did not differ. However, liver IGF-I expression in SLS affected lambs was nearly double that of control lambs (P<0.01). These data suggest that the regulation of IGF-I and the IGF-BPs may be involved in the physical manifestations of this disorder.