Investigation into the inheritance and biochemistry of chondrodysplasia in Texel sheep : a thesis presented in partial fulfilment of the requirements for the Master of Science at Massey University, Palmerston North, New Zealand
A skeletal chondrodysplasia characterized by dwarfism and angular deformity of the forelimbs has been recognized over four seasons in Texel and Texel cross lambs on three related properties. Some affected lambs have normal co-twins indicating that the disease is not dietary, but likely to be the result of a genetic disorder. This study reports on the inheritance and biochemistry of this newly discovered chondrodysplasia in Texel sheep. The outcome of a backcross trial between putative carrier ewes and affected rams provided evidence that indicated that the chondrodysplasia has an autosomal recessive mode of inheritance, and that it is likely to be caused by a single gene defect. Analysis of proteoglycan constituents of cartilage by SDS-PAGE, followed by sulfate-specific staining indicated that the biochemical abnormality lies in the level of sulfation of proteoglycans in the extracellular matrix of affected animals. It was also shown by SDS-PAGE that there were no differences in the major collagen constituents of cartilage between unaffected and affected animals. A candidate gene, the diastrophic dysplasia sulfate transporter, was determined based on its involvement in the process of sulfation of proteoglycans and its involvement in characterized human dysplasias, which resemble Texel chondrodysplasia both phenotypically and biochemically. PCR amplification and sequencing of 85.4 % of this gene revealed no nucleotide differences between the exonic DNA of normal, carrier, and affected animals. While this reduced the likelihood that this gene is causative in the chondrodysplasia, it does not eliminate it as a candidate, based on the fact that a mutation may exist in the region not sequenced, including the possibility of splice site mutations.