COL4A3 and posterior polymorphous corneal dystrophy: All mutations lead to abnormalities in the basement membrane of the glomerulus, cochlea, retina, lens capsule, and cornea, which eventually contribute to the typical phenotype of Alport syndrome.1 Recently, the presence of a complex (core plus secondary) binding site for TCF8 in the promoter of Alport syndrome gene COL4A3, which encodes collagen type IV alpha 3 is thought to cause posterior polymorphous dystrophy.10