Genetic test for myophosphorylase deficiency in Charolais cattle

Objective - To develop a simple test for the determination of genetic susceptibility to myophosphorylase deficiency in Charolais cattle. Animals - 48 adult Charolais cattle and 233 calves from one herd and 3 Charolais cattle from 2 other herds. Sixty Piedmontese and 34 Saler cattle provided negative-control samples. Procedure - Cattle were from a Charolais herd in which myophosphorylase deficiency was identified and 2 other herds in which cattle had signs compatible with the disease. Genomic DNA was isolated from neparinized blood samples. A segment of the myophosphorylase gene containing the mutation site was amplified by polymerase chain reaction assays, and the genotype (normal vs affected allele) was determined by using restriction enzyme and agarose gel electrophoretic analysis. Results - The 3 myophosphorylase genotypes (homozygous normal, homozygous affected, and heterozygous) could be readily identified. Segregation of the affected allele could be determined in an extended pedigree, and all clinically affected cattle were homozygous for this allele. Determination of the distribution of normal and affected alleles in a large population did not indicate a strong selective advantage for heterozygous carriers in this herd. Heterozygotes were also identified in Charolais cattle from the 2 other herds. Conclusions - Breeders of Charolais cattle can use this genetic test to perform marker-assisted selection and remove cattle with the mutant myophosphorylase allele from the breeding population. Alternatively, they could more accurately determine selective advantages and disadvantages for cattle with the affected allele. Clinical Relevance - Development of this test enables rapid genetic screening of Charolais and related breeds of cattle for detection of the mutation responsible for myophosphorylase deficiency.