UC Davis

Anhidrosis is defined as a decreased or absent ability to sweat in response to heat and exercise. In horses, this condition can increase the risk of life-threatening hyperthermia. A prior study has suggested that equine anhidrosis is associated with a missense variant (rs68643109) in the Potassium Voltage-Gated Channel Subfamily E Regulatory Subunit 4 (KCNE4) gene. This project aimed to validate this association in a population of well-phenotyped horses and to determine the allele frequency of this variant in publicly available whole-genome sequence data. Fifty horses within the University of California Davis Center for Equine Health herd were evaluated for anhidrosis using a series of intradermal terbutaline injections. From existing whole-genome sequence data, the rs68643109 genotype of each horse was identified. When stimulated with terbutaline, all 50 horses produced sweat. All three genotypes at rs68643109 were present in this population of horses; the allele previously associated with anhidrosis (G) was present at a frequency of 0.72. No statistical difference in total sweat score was found (p = 0.31). In whole-genome sequences from 820 other horses reported across three prior studies, the alternative (candidate) allele frequency was similarly high, ranging from 0.52 to 0.68. Since all 50 horses tested in our population produced sweat regardless of genotype, and the previously associated allele is present at a high frequency across datasets, these data fail to validate the missense variant within the KCNE4 gene as causative of or contributing to equine anhidrosis.