ZEB1 and posterior polymorphous corneal dystrophy: PPCD is genetically heterogeneous: PPCD1 (OMIM #122000) is caused by mutations in the OVOL2 promoter [3], PPCD2 (OMIM #609140) has been associated with mutations in COL8A2 [4] and PPCD3 (OMIM #609141) with mutations in ZEB1 genes [5].