A second KRT71 allele in curly coated dogs.

Major characteristics of coat variation in dogs can be explained by variants in only a few genes. Until now, only one missense variant in the KRT71 gene, p.Arg151Trp, has been reported to cause curly hair in dogs. However, this variant does not explain the curly coat in all breeds as the mutant 151 Trp allele, for example, is absent in Curly Coated Retrievers. We sequenced the genome of a Curly Coated Retriever at 22× coverage and searched for variants in the KRT71 gene. Only one protein-changing variant was present in a homozygous state in the Curly Coated Retriever and absent or present in a heterozygous state in 221 control dogs from different dog breeds. This variant, NM_001197029.1:c.1266_1273delinsACA, was an indel variant in exon 7 that caused a frameshift and an altered and probably extended C-terminus of the KRT71 protein NP_001183958.1:p.(Ser422ArgfsTer?). Using Sanger sequencing, we found that the variant was fixed in a cohort of 125 Curly Coated Retrievers and segregating in five of 14 additionally tested breeds with a curly or wavy coat. KRT71 variants cause curly hair in humans, mice, rats, cats and dogs. Specific KRT71 variants were further shown to cause alopecia. Based on this knowledge from other species and the predicted molecular consequence of the newly identified canine KRT71 variant, it is a compelling candidate causing a second curly hair allele in dogs. It might cause a slightly different coat phenotype than the previously published p.Arg151Trp variant and could potentially be associated with follicular dysplasia in dogs.

A frameshift variant in the EDA gene in Dachshunds with X-linked hypohidrotic ectodermal dysplasia.

X-linked hypohidrotic ectodermal dysplasia (XLHED) is a genetic disease characterized by hypoplasia or absence of hair, teeth and sweat glands. The EDA gene, located on the X chromosome, encodes the type II transmembrane protein ectodysplasin A. Variants in the EDA gene can lead to XLHED in humans, mice, cattle and dogs. In the present study, we investigated a litter of Dachshund puppies, of which four male puppies showed clinical signs of XLHED. We performed a candidate gene analysis in one affected puppy and several non-affected relatives. This analysis revealed a single base-pair deletion in the coding sequence of the EDA gene in the affected puppy (NM_001014770.2:c.842delT). The deletion is predicted to cause a frameshift, NP_001014770.1:p.(Leu281HisfsTer22), leading to a premature stop codon which truncates more than one quarter of the EDA protein. Sanger sequencing results confirmed that this variant was inherited from the dam. Based on knowledge about the functional impact of EDA variants in dogs and other species, c.842delT is a convincing candidate causative variant for the observed XLHED in the male puppies.

Two MC1R loss-of-function alleles in cream-coloured Australian Cattle Dogs and white Huskies.

Loss-of-function variants in the MC1R gene cause recessive red or yellow coat-colour phenotypes in many species. The canine MC1R:c.916C>T (p.Arg306Ter) variant is widespread and found in a homozygous state in many uniformly yellow- or red-coloured dogs. We investigated cream-coloured Australian Cattle Dogs whose coat colour could not be explained by this variant. A genome-wide association study with 10 cream and 123 red Australian Cattle Dogs confirmed that the cream locus indeed maps to MC1R. Whole-genome sequencing of cream dogs revealed a single nucleotide variant within the MITF binding site of the canine MC1R promoter. We propose to designate the mutant alleles at MC1R:c.916C>T as e1 and at the new promoter variant as e2 . Both alleles segregate in the Australian Cattle Dog breed. When we considered both alleles in combination, we observed perfect association between the MC1R genotypes and the cream coat colour phenotype in a cohort of 10 cases and 324 control dogs. Analysis of the MC1R transcript levels in an e1 /e2 compound heterozygous dog confirmed that the transcript levels of the e2 allele were markedly reduced with respect to the e1 allele. We further report another MC1R loss-of-function allele in Alaskan and Siberian Huskies caused by a 2-bp deletion in the coding sequence, MC1R:c.816_817delCT. We propose to term this allele e3 . Huskies that carry two copies of MC1R loss-of-function alleles have a white coat colour.