COL4A3 and posterior polymorphous corneal dystrophy: This highlights another example of genetic heterogeneity that results in a variety of phenotypic presentations, like that of TGFBI. A heterozygous frameshift mutation in ZEB1 was found to induce ectopic expression of COL4A3 by corneal epithelial cells in PPCD, implicating COL4A3 as a possible target of ZEB1 regulation.140