On average, participants with heterozygous RB1 variants were diagnosed with retinoblastoma at a younger age compared with participants with somatic disease (mean [SD], 0.7 [0.6] vs 1.8 [1.7] years; difference, 1.1 [95% CI, 0.6-1.6] years; P < .001) and those with RB1 mosaicism (mean [SD], 0.7 [0.6] vs 1.9 [1.8] years; difference, 1.2 [95% CI, 0.6-1.7] years; P < .001) (eTable 1 in Supplement 1). Here, RB1 is linked to retinoblastoma.