Inheritance of a new mutation affecting muscle weakness within a common haplotype in Holsteins
A haplotype associated with calf recumbency and mortality having a recessive effect but apparent incomplete penetrance was previously linked to the end of chromosome 16 (78.7 to 80.7Mbp). Genotype analysis of 5.6 million Holsteins indicated that the haplotype was common and traced back to 1952, with a key ancestor born in 1984 (HOUSA1964484, Southwind) identified from chip genotypes as homozygous for the suspect haplotype. Sequence data from Southwind, an affected calf, and the sire of the affected calf were scanned for candidate mutations. A mutation in the CACNA1s gene causing symptoms of recumbency (lately termed Holstein Early Onset Muscle Weakness; HMW) was homozygous in the affected calf and heterozygous in the calf’s sire and Southwind. Improved methods for using pedigree to track new mutations within existing haplotypes were developed, and gene tests for the mutation were also included. For new mutations within existing common haplotypes, determining carrier status without gene tests is difficult, even with accurate pedigrees when the original haplotype has a high frequency.
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