Initial candidate gene‐based attempts to map the causative locus for OM examined 11 genes known to have a role in melanocyte and melanosome development or known to be associated with other pigmentation‐related diseases; this included a pair of genes (Gpnmb and Tyrp1) which have known mouse genetic variants that, together, produce a mouse phenotype (DBA/2J) with similar histopathological changes to OM as seen in Cairn Terriers.7, 8. The gene discussed is GPNMB; the disease is ocular melanoma.