Frequency of the allelic variant of the ptpla gene responsible for centronuclear myopathy in Labrador retriever dogs as assessed in Italy

Centronuclear myopathy (CNM) is an autosomal recessive hereditary disease affecting Labrador Retriever dogs. The disease is characterized by muscle lesions, typically encompassing reduction in the number and atrophy of type II fibers, and is caused by a short interspersed repeat element insertion in exon 2 of the protein tyrosine phosphatase-like member A. The actual allele frequency is unknown; a study was undertaken to ascertain it using a convenience-sample population composed of 217 Labrador Retrievers. In addition to 3 subjects already diagnosed with CNM, used as positive controls for polymerase chain reaction, only 2 unrelated dogs were heterozygous wild-type/mutation (wild-type/mut). Thus, the frequency of the CNM allele observed in the present study was 1.8% and 0.47% when including and excluding the 3 mut/mut homozygous cases, respectively. Based on the Hardy-Weinberg exact test (P 5 1.00), the genotype frequency without the CNM-affected dogs was in agreement with the Hardy-Weinberg equilibrium. Assuming the Hardy-Weinberg equilibrium law, the expected frequency of the homozygous mutated genotype was calculated to be approximately 0.00005, which corresponds to 1 case of CNM out of 20,000 dogs. In conclusion, the present study indicates that the CNM allele is present but rare in a convenience sample of Labrador Retrievers in Italy.