This model accounts for the ability of B6D2F1 [20] or D2-Gpnmb+ (Fig. 2) bone marrow to suppress the D2 iris disease (because bone derived cells with wild-type Gpnmb alleles do not respond abnormally to the debris resulting from the melanosomal insults and mild iris damage). The gene discussed is GPNMB; the disease is iris disorder.