GRHL2 and posterior polymorphous corneal dystrophy: Despite these recent advances in our understanding of the molecular basis of PPCD, there is evidence for further genetic heterogeneity of PPCD.12, 21, 23 Here, we describe an additional PPCD locus, PPCD4, which was mapped to 8q22.3–q24.12, and the subsequent identification of causative non-coding variants in GRHL2 with further evidence for the importance of MET in PPCD.