We isolated both normal and tumor tissue from three RP heterozygous mutant lines, hi10, hi258, and hi1974, each of which showed a reduction in expression of its respective RP mutant gene of 10-fold or more (Figure 4A) and examined DNA from these samples for the presence of the mutant and wild-type RP alleles by PCR (Figure 4B). The gene discussed is BLOC1S3; the disease is neoplasm.