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.

Primary congenital glaucoma (PCG), a rare, severe and blinding disease, usually results from mutations in the CYP1B1 gene located in chromosome 2p22.2. Uniparental isodisomy (UPID) is also a rare condition in which a diploid offspring carries two identical copies of a single parental chromosome. By DNA sequence analysis, we found that a proband (female newborn) affected by PCG was homozygous for the null-allele F261L of the CYP1B1 gene. Her father was a heterozygous carrier for this mutation, and unexpectedly her mother carried only the G168D mutation in the heterozygous state. Segregation analysis of eight microsatellite markers which spanned the two arms of chromosome 2 was consistent with paternal isodisomy for this chromosome in the proband. To the best of our knowledge, this is the first reported case of UPID resulting in PCG and the fifth reported case of paternal UPID for chromosome 2. In addition, the absence of a clinical phenotype other than PCG confirms previous observations of there being no paternally imprinted genes in chromosome 2 that have major phenotypic effects. These results, along with previous reports, also suggest that UPID may play a relevant role in recessive diseases linked to chromosome 2.