In Russian breeds, there is a number of polymorphic variants,in homozygous state causing hereditary diseases, some ofwhich (mutations in the genes F11, IARS and NHLRC2) havealready been discussed above due to their breed specificity.Also, the variants in the ROR2 and LRP4 genes should bementioned that are associated with the manifestation ofinterdigital hyperplasia (proliferation of tissue between thehooves) and syndactyly (fusion of the fingers, also called ‘mulefoot’), respectively. This evidence concerns the gene ROR2 and hereditary disease.