In some retinoblastoma patient samples, the capacity of miR-191 to engage MDM4 mRNA is eliminated by somatic mutations (SNPs) that eliminate this miR binding site (as discussed in Section ‘MDM4 SNPs and cancer risk.’); while in others miR-191 levels are lower than in the normal fetal retinae (McEvoy et al., 2012). The gene discussed is MDM4; the disease is retinoblastoma.