H-Locus (Harlequin)

Description

The H-Locus test looks for the variant that causes the harlequin coat pattern in Great Danes. Harlequin is a coat pattern recognized only in Great Danes, and it is caused by a mutation in the PSMB7 gene. The harlequin pattern is the result of a complex interaction between variants at the merle and harlequin loci (the M-Locus and H-Locus). The harlequin variant acts as a modifier of merle. All harlequin dogs must have one or two copies of the mutation responsible for the merle pattern. The harlequin pattern cannot be expressed in dogs that are not merle or that have only red pigment.

The dominant merle gene produces a coat of dark spots on a diluted background. If a merle dog also inherits a single copy of the harlequin gene, the dark spots increase in size and the background pigment is eliminated, leaving dark patches on a white coat.

Harlequin is presumed to be homozygous embryonic lethal. This means that an embryo that inherits two copies of the harlequin allele (H/H) typically does not survive to birth. No animals have been observed with two copies of the mutated gene. Therefore, all harlequin-patterned dogs have only one copy of the mutated gene (n/H), and every dog is either n/n for harlequin (no harlequin pattern) or n/H.

A dog can carry the harlequin mutation without showing the pattern. According to research conducted by Dr. Leigh Anne Clark at Clemson University, over 59% of harlequin-bred black or non-merle dogs (including those with the mantle coloration) carry the harlequin mutation.

Possible results

Breeds Affected

Great Dane

Reference

Genome-wide linkage scan localizes the harlequin locus in the Great Dane to chromosome 9.

[PMID: 18513894]

A missense mutation in the 20S proteasome β2 subunit of Great Danes having harlequin coat patterning.

[PMID: 21256207]