Other examples of autosomal dominant conditions where the degree of clinical penetrance is modulated by differential expression of the wild-type and mutant alleles include hereditary elliptocytosis (SPTA1, Wilmotte et al. 1993), Marfan syndrome (FBN1, Hutchinson et al. 2003), retinoblastoma (RB1, Taylor et al. 2007), colorectal cancer (APC, Yan et al. 2002; TGFBR1, Valle et al. 2008) and breast and ovarian cancer (BRCA1, Ginolhac et al. 2003). This evidence concerns the gene RB1 and retinoblastoma.