Cocoa

Description

Variants in the TYRP1 gene, or B-Locus, are the most common cause of brown, chocolate or liver coat color. There are currently five known TYRP1 mutations that affect how the gene works, and they explain the majority of dogs with brown coat and nose color. One exception is the brown or chocolate French Bulldog, whose cause remained a mystery for years. In 2014 Animal Genetics sequenced the TYRP1 gene of several brown French Bulldogs but did not find any functional variants that corresponded to brown coat color, eliminating TYRP1 as the primary cause of French Bulldog chocolate.

In 2020, research conducted at the University of Bern in Switzerland revealed a nonsense variant in the HPS3 gene, c.2420G>A or p.(Trp807*). In that study the brown or chocolate dogs were homozygous for the mutant allele. This color is known as “cocoa.”

Animal Genetics conducted whole genome sequencing on three brown or chocolate French Bulldogs: two that were negative for all TYRP1 mutations and one that carried one copy of a recessive TYRP1 variant. Our research showed the same correlation between the recessive HPS3 allele and the appearance of the dog.

The differences in coat, skin and eye color between TYRP1 brown and HPS3 cocoa dogs are subtle but clear. Dogs with two copies of cocoa have a slightly darker coat color and lighter eyes than the more common TYRP1-related brown dogs.

Possible results

Breeds Affected

French Bulldog

Reference

Novel Brown Coat Color (Cocoa) in French Bulldogs Results from a Nonsense Variant in HPS3.

[PMID: 32526956]

Related Tests

• B-Locus (Brown, Chocolate) — the common cause of brown, chocolate and liver
• D-Locus (Dilute) — the dilution gene behind blue and lilac
• Albinism (Pink) — the variant known as pink in French Bulldogs