In the latter case, L/M cone precursors lacking the retinoblastoma protein (pRB) were shown to proliferate in a manner dependent on the L/M-cone lineage factors RXRγ and TRβ2 and the intrinsically highly expressed MDM2 and MYCN oncoproteins, likely representing the first step of retinoblastoma tumorigenesis (Cobrinik, 2024; Xu et al., 2009; Xu et al., 2014; Singh et al., 2018). The gene discussed is RB1; the disease is retinoblastoma.