Additional Evidence Fails to Associate Variation in KCNE4 With Equine Anhidrosis.

Overview

• This research investigated whether a specific genetic variant (KCNE4) is linked to equine anhidrosis (a condition where horses fail to sweat properly).
• The study found no evidence supporting a connection between this genetic variation and the disease based on extensive testing and genetic analysis.

Background

• A previous genome-wide association (GWA) study involving 200 horses (Thoroughbreds and stock horses) suggested that chromosome 6 might be linked to equine anhidrosis.
• A specific missense variant in the KCNE4 gene was proposed as a potential risk allele related to this condition.
• Initial annotations and protein modeling from the earlier study suggested the G allele increased risk, while later indications implied the A allele might be the risk factor instead.

Objectives and Rationale

• The current study aimed to clarify and reassess the association between the KCNE4 variant alleles (A or G) and equine anhidrosis.
• Researchers used more precisely phenotyped horses, utilizing an intradermal terbutaline sweat test (ITST) to categorize sweating ability accurately.
• The study also explored linkage disequilibrium (LD), which is the genetic co-inheritance probability between the KCNE4 variant and nearby genetic markers implicated in the GWA results, to check for true genetic association.

Methods

• Genotyping of 20 Thoroughbred horses tested by ITST was performed, including 9 horses with partial or complete anhidrosis.
• Clinical cases (n=4) of equine anhidrosis were similarly genotyped to assess allele presence.
• Whole-genome sequencing data from 2 horses (case and control) previously used in the original publication was analyzed for genotype status at the KCNE4 locus and the GWA single nucleotide variant (SNV).
• Publicly available genetic data sets of 897 horses and a subgroup of 369 Thoroughbreds were examined to evaluate linkage disequilibrium (LD) between the KCNE4 variant and the GWA SNV (rs68656009).
• Restriction of the analysis to the 85 Thoroughbreds included in the original GWA balanced previous sample characteristics.

Key Findings

• No significant association was found between the KCNE4 A allele and equine anhidrosis when the phenotype was treated as either binary (affected vs non-affected) or when considering partial versus complete anhidrosis status (p-values of 0.16 and 0.21, respectively).
• The clinical cases showed no pattern linking alleles at KCNE4 with anhidrosis: the genotype distribution was AA = 1, AG = 1, and GG = 2.
• Whole-genome sequence analysis showed both case and control horses were homozygous for the A allele at KCNE4, but the case was heterozygous for the GWA SNV, suggesting no direct linkage.
• LD between the KCNE4 variant and the GWA SNV was low in the broader population (r = 0.19) and moderate but insufficient in Thoroughbreds (r = 0.58).
• In the subset of 85 Thoroughbreds originally studied via GWA, no convincing association of chromosome 6 with anhidrosis was detected.

Conclusions

• The data collectively do not support the KCNE4 missense variant or the initially implicated GWA single-nucleotide variant on chromosome 6 as risk factors for equine anhidrosis.
• This suggests that previous associations may have been spurious or due to confounding factors in the original study populations.
• More comprehensive genetic or functional studies are needed to clarify the genetic basis of equine anhidrosis.

Implications

• Veterinarians and breeders should be cautious about using KCNE4 variants as markers for breeding decisions related to sweat disorders in horses.
• Understanding that the KCNE4 variant is not linked to anhidrosis helps redirect research efforts toward identifying other genetic or environmental causes.