Posterior polymorphous dystrophy (Fig 6-3) is another endothelial dystrophy that may be inherited in autosomal dominant or recessive fashion, with the mutation mapped to 20q11. In this condition, the endothelium has epithelial-like characteristics. These include multilayering, which may be seen histologically on routine light microscopy, and microvilli, which are best demonstrated on electron microscopy. The total number of endothelial cells may be decreased. Variable thickening of the Descemet membrane and guttae may be observed. There may also be secondary glaucoma, either open-angle or associated with iridocorneal adhesions. The resultant corneal clouding is typically central, but the degree of opacification varies greatly, with some patients never requiring corneal transplantation and others requiring keratoplasty in childhood or even infancy. See also BCSC Section 8, External Disease and Cornea.