Harlequin Pattern in Great Danes

Harlequin is a coat pattern with distinctive dark patches on a white background. Harlequin is a genetically complex coloration resulting from heterozygous mutations at two loci: merle and harlequin. While the merle (Mm) genotype alone, caused by the SILV mutation, causes a more colourful pattern characterised by dark patches on a dilute background, when combined with the harlequin (Hh) genotype, which is its dominant modifier, the dilute pigment is removed, and the size of the fully pigmented areas is increased. This colouration is caused by the c.146T>G missense mutation in the PSMB7 gene, which encodes the β2 catalytic subunit of the proteasome.

Inheritance of the mutation is autosomal dominant. One copy of the mutant gene inherited from either parent is sufficient to cause harlequin pattern. Homozygosity (HH) is embryonic lethal.

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Reference:

Clark, LA., Tsai, KL., Starr, AN., Nowend, KL., Murphy, KE. : A missense mutation in the 20S proteasome β2 subunit of Great Danes having harlequin coat patterning. Genomics 97:244-8, 2011. Pubmed reference: 21256207