Functional analysis of CYP1B1 mutations and association of heterozygous hypomorphic alleles with primary open-angle glaucoma

Lopez-Garrido M-P, Blanco-Marchite C, Sanchez-Sanchez F, Lopez-Sanchez E, Chaques-Alepuz V, Campos-Mollo E, Salinas-Sanchez AS, Escribano J. Functional analysis of CYP1B1 mutations and association of heterozygous hypomorphic alleles with primary open-angle glaucoma. Glaucoma is an inherited complex and heterogeneous disease, and one of the most prevalent causes of definitive blindness in the world. Recent reports have indicated that heterozygous mutations of the CYTOCHOROME P4501B1 (CYP1B1) gene are present in 4–10% of patients with primary open-angle glaucoma (POAG). To further evaluate the role of CYP1B1 mutations in POAG we extended our previous association study and carried out a functional analysis of the mutations identified by polymerase chain reaction (PCR) DNA sequencing of the three exons of the gene in a total of 245 unrelated Spanish patients and 326 control subjects. Eight of nine different mutations identified in these patients were cloned and functionally assessed by measuring ethoxyresorufin O-deethylation activity and CYP1B1 stability in transiently transfected HEK-293T cells. All these mutants showed reduced catalytic activity, ranging from 20% to 60% of wild-type and/or decreased protein stability and, therefore, they were classified as hypomorphic alleles. No null alleles were identified in these patients. We found heterozygous hypomorphic CYP1B1 mutations in 17 (6.7%) patients and in seven controls (2.1%) showing that these mutations are associated with an increased risk of POAG (p = 0.005; odds ratio = 3.2; 95% confidence interval = 1.30–9.19). Our data suggest that hypomorphic CYP1B1 mutations are, to date, the main known genetic risk factor in POAG.