A histologic categorization of aqueous outflow routes in familial Open-Angle glaucoma and associations with mutations in the MYOC gene in Japanese patients

PURPOSE. This study evaluated specific relationships between pathogenic mechanisms and genetic polymorphisms in primary open-angle glaucoma (POAG). We analyzed the morphologies of trabeculectomy specimens obtained from patients with familial POAG. METHODS. We used light microscopy and transmission electron microscopy to examine specimens obtained from 17 eyes of 14 patients with familial POAG. We also conducted exome analyses of two families and used targeted Sanger sequencing to analyze samples obtained from the remaining patients. RESULTS. The POAG cases examined in this study were divided into two groups based on morphologic characteristics. Group A eyes (7 eyes from 5 patients) had an abnormally thick trabecular meshwork (TM), whereas group B eyes (10 eyes from 9 patients) had a TM of normal thickness. The characteristics of the outflow routes in group A eyes were remarkable and included apoptotic TM cells, abnormally thickened TM basement membranes, fused TM beams, and occluded Schlemm’s canals. All group A patients harbored mutations (F369L, P370L, T377M, and T448P) in the myocilin (MYOC) gene that were not found in group B patients. CONCLUSIONS. Although age matching of morphologic changes in the outflow routes was impossible due to the small sample size, this study suggests that abnormal TM cells may cause sequential damage in abnormally thickened TM basement membranes, TM cell apoptosis, TM beam fusion, and the occlusion of Schlemm’s canals. The four detected MYOC mutations appeared to be associated with morphologic changes in the TM and the underlying pathogenesis of a subtype of familial POAG.