Optic nerve degeneration caused by glaucoma is a leading cause of blindness worldwide. Patients affected by the normal-pressure form of glaucoma are more likely to harbor risk alleles for glaucoma-related optic nerve disease. We have performed a meta-analysis of two independent genome-wide association studies for primary open angle glaucoma (POAG) followed by a normal-pressure glaucoma (NPG, defined by intraocular pressure (IOP) less than 22 mmHg) subgroup analysis. The single-nucleotide polymorphisms that showed the most significant associations were tested for association with a second form of glaucoma, exfoliation-syndrome glaucoma. The overall meta-analysis of the GLAUGEN and NEIGHBOR dataset results (3,146 cases and 3,487 controls) identified significant associations between two loci and POAG: the CDKN2BAS region on 9p21 (rs2157719 [G], OR = 0.69 [95%CI 0.63–0.75], p = 1.86×10−18), and the SIX1/SIX6 region on chromosome 14q23 (rs10483727 [A], OR = 1.32 [95%CI 1.21–1.43], p = 3.87×10−11). In sub-group analysis two loci were significantly associated with NPG: 9p21 containing the CDKN2BAS gene (rs2157719 [G], OR = 0.58 [95% CI 0.50–0.67], p = 1.17×10−12) and a probable regulatory region on 8q22 (rs284489 [G], OR = 0.62 [95% CI 0.53–0.72], p = 8.88×10−10). Both NPG loci were also nominally associated with a second type of glaucoma, exfoliation syndrome glaucoma (rs2157719 [G], OR = 0.59 [95% CI 0.41–0.87], p = 0.004 and rs284489 [G], OR = 0.76 [95% CI 0.54–1.06], p = 0.021), suggesting that these loci might contribute more generally to optic nerve degeneration in glaucoma. Because both loci influence transforming growth factor beta (TGF-beta) signaling, we performed a genomic pathway analysis that showed an association between the TGF-beta pathway and NPG (permuted p = 0.009). These results suggest that neuro-protective therapies targeting TGF-beta signaling could be effective for multiple forms of glaucoma.

Posterior polymorphous corneal dystrophy (PPCD, also known as PPMD) is a rare disease involving metaplasia and overgrowth of corneal endothelial cells. In patients with PPCD, these cells manifest in an epithelial morphology and gene expression pattern, produce an aberrant basement membrane, and, sometimes, spread over the iris and nearby structures in a way that increases the risk for glaucoma. We previously mapped PPCD to a region (PPCD3) on chromosome 10 containing the gene that encodes the two-handed zinc-finger homeodomain transcription factor TCF8. Here, we report a heterozygous frameshift mutation in TCF8 that segregates with PPCD in the family used to map PPCD3 and four different heterozygous nonsense and frameshift mutations in TCF8 in four other PPCD probands. Family reports of inguinal hernia, hydrocele, and possible bone anomalies in affected individuals suggest that individuals with TCF8 mutations should be examined for nonocular anomalies. We detect transcripts of all three identified PPCD genes (VSX1, COL8A2, and TCF8) in the cornea. We show 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, and we present immunohistochemical evidence of ectopic expression of COL4A3 in corneal endothelium of the proband of the original PPCD3 family. Identification of TCF8 as the PPCD3 gene provides a valuable tool for the study of critical gene regulation events in PPCD pathology and suggests a possible role for TCF8 mutations in altered structure and function of cells lining body cavities other than the anterior chamber of the eye. Thus, this study has identified TCF8 as the gene responsible for approximately half of the cases of PPCD, has implicated TCF8 mutations in developmental abnormalities outside the eye, and has presented the TCF8 regulatory target, COL4A3, as a key, shared molecular component of two different diseases, PPCD and Alport syndrome.