Variants of the Myocilin Gene in Japanese Patients with Normal-Tension Glaucoma

Myocilin <i>(MYOC)</i> mutations are associated with juvenile- and adult-onset primary open-angle glaucoma (POAG). The purpose of this study was to determine whether <i>MYOC</i> gene mutations are associated with normal-tension glaucoma (NTG). The prevalence of <i>MYOC</i> mutations was determined in 80 Japanese NTG patients and 100 control subjects. In addition, the expression of mutant <i>MYOC</i> was determined by transforming COS-1 cells with five myocilin variants (R158Q, D208E, I360N, A363T, and I477S) and examining whether myocilin was present in the cultured cells and/or the culture medium by western blotting. Six different nucleotide sequence variants, R46Stop, R76K, R158Q, D208E, A488A, and one in the 3′ non-coding region, were identified in 80 NTG patients. Variants in codon 46 (R46Stop), codon 158 (R158Q), and codon 488 (A488A) were not found in the 100 normal controls. The frequency of other sequence changes (R76K, D208E, and 3′ non-coding) in NTG patients did not differ significantly from the frequencies in the control subjects. COS-1 cells transfected with the wild type, R158Q, or D208E variants secreted myocilin into the culture medium. On the other hand, the detected myocilin was significantly reduced in the medium of cells transfected with the I360N, A363T, or I477S variants that were previously identified as mutations for POAG. Definitive evidence of <i>MYOC</i> variants associated with NTG was not found.