TYRP1 and iris disorder: Mutations in two D2 genes [tyrosinase-related protein 1 (Tyrp1) and glycoprotein (transmembrane) nmb (Gpnmb)] have been shown to induce a depigmenting iris disease (hereafter referred to as iris disease) characterized by abnormal liberation of iris pigment into the ocular anterior chamber (Anderson et al., 2002; Chang et al., 1999).