Analysis of CYP1B1 Gene Mutations Spectrum in Families with Open-Angle Glaucoma in Calabar, Nigeria

Background: Primary open-angle glaucoma is one of the commonest causes of blindness due to optic nerves damage because of elevated intraocular pressure and it is the commonest form of glaucoma. We determined the frequency of CYP1B1 gene mutations spectrum among families with open-angle glaucoma in Calabar.

Methods: Ophthalmologists examined the recruited subjects to establish the diagnosis on patients. Ninety-six (96) subjects were recruited, comprising 15 primary open-angle glaucoma patients, 11 primary childhood glaucoma patients, 17 parents and 53 healthy unrelated, aged-matched controls were selected from individuals attending the eye clinic. 2-3 ml of blood was collected from each participant, DNA extracted, PCRs and bidirectional sequencing performed on all subjects for CYP1B1 mutation on exon 3. The nucleotide sequences of the CYP1B1 gene were edited from chromatograms using the Bio edit software. Multiple sequence alignment and pairwise comparison of CYP1B1 gene was carried out on MEGA 6.06 software. GORIV software was used in determining the secondary structure for each individual with and without the CYP1B1 gene mutation. Phyre2 software was utilized for predicting the 3D tertiary structure for individuals. Statistical analyses were performed using SPSS version 20.0 software. Significant level was set at P<0.05.

Results: CYP1B1 gene were amplified and sequenced from all recruited participants for this study. The mean age of primary childhood glaucoma was 98.36±12.43 months and 56.44±7.1 years for POAG, while the mean age at disease presentation of 43.42±1.4 months and 52.33±7.4 years for primary childhood glaucoma and POAG, respectively. The mean intraocular pressure (IOP) in right/left eye was 24/23 mmHg and 32.1/31 mmHg for primary childhood glaucoma and POAG, respectively. All cases of glaucoma were bilateral. Two non-synonymous mutations (g.291G>C, g344C>T) and 3 synonymous mutations (g.1T>C, g.1T>G, g.46T>C) of CYP1B1 gene mutations spectrum were observed in primary childhood glaucoma, POAG and parents. The g.291G>C (p.Q97H) recorded the frequency of 36.4%, 33.3% and 29.4% for primary childhood glaucoma, POAG patients and parents respectively. Eight different nucleotides deletions including g.2-4delCTC, g.2delC, g.317delT, g.535delG, g.378-380delATG, and others were detected. The deletion g.370-380delATG frequency was 27.3%, 20.5%, and 41.2% for primary childhood glaucoma, POAG patients and parents respectively. The CYP1B1 gene mutations spectrums were not detected in all controls.

Conclusion: This research identified CYPIBI gene mutations spectrum, which were detected in primary childhood glaucoma, POAG cases and parents but not observed in controls. It suggests molecular genetics etiology of the disease in Calabar population, but further studies are required. This will forms baseline information for further molecular studies among glaucoma patients in Nigeria.