PITX3 and anterior segment dysgenesis: 640_656dup (p.Gly220ProfsX95) of the PITX3 gene is the main gene mutation that causes ASMD; however, the number of ASMD cases is relatively small, and the ocular involvement of heterozygous patients is highly variable, suggesting that the penetrance of PITX3 mutation is not complete, which may be due to the changes in the protein activity at different developmental stages caused by the stochasticity during development, the influence of gene modifications, and the intrauterine environment.