The mutation responsible for the cocoa colour in the French bulldog has been identified in the Hermansky-Pudlak syndrome 3 (HPS3) gene. Dogs homozygous for this mutation are a shade darker brown than dogs mutated for brown (Locus B). In humans and mice, mutations in the HPS3 gene are associated with symptoms such as visual impairment, abnormal eye pigmentation and bleeding. These effects of the mutation have not been reported in dogs homozygous for the cocoa variant. ogs with two copies of the cocoa variant can be cocoa, however the final colour of the dog also depends on other genes controlling coat colour.
