GPNMB and pigment dispersion syndrome: The first identified locus linked to the pigment dispersion syndrome phenotype, PDS1, is located at 7q35-36.[19] A second locus, PDS2, was mapped to 18qll-q22.[89] Two genes in the mouse contribute to the disease: TYRP1 (Tyrosinase related protein 1) and Gpnmb (Glycoprotein NMB).