Genomic Characterization of TBK1 Duplication in Korean Normal Tension Glaucoma Patients

PReCIS:: One (0.2%) out of 418 Korean NTG patients had TBK1 duplication.The putative mechanism of TBK1 duplication in Korean NTG patients is the non-homologous end-joining. PURPOSE: TBK1 duplication is a genomic cause of familial normal tension glaucoma (NTG). NTG accounts for up to 90% of primary open-angle glaucoma in Koreans, with genetic tendency. We aimed to investigate the prevalence of TBK1 duplication in Korean NTG patients and to identify their genomic structure and duplication mechanism. MATERIALS AND METHODS: We obtained DNA samples from 418 NTG patients and 195 healthy controls for evaluating TBK1 copy number variations using semi-quantitative PCR. The samples with TBK1 gene duplication were further confirmed using droplet digital PCR (ddPCR). The whole genome sequencing of patient samples with duplications was performed to identify the accurate breakpoints and to elucidate genomic structure. Ophthalmic evaluation and confirmation of TBK1 duplication using junction PCR were performed in families of positive patients. RESULTS: TBK1 duplication was found in 1 out of 418 NTG cases (0.2%). The duplication range was from g.64,803,151 to g.64,927,214 (124,06350% shaded blockbp). It is the smallest region of overlapping duplication in TBK1. Any repetitive sequences were not found near the breakpoints of our case. Inserted sequences were found within the breakpoints. A brother and a niece of the positive case appeared the typical clinical features of NTG and shared the same TBK1 duplications with the index case. CONCLUSION: In Korea, prevalence of TBK1 duplication was 0.2% and the smallest reported TBK1 duplication associated with NTG was found. The mechanism of TBK1 duplication was suggested to be non-homologous end joining while a previous report pointed out the mechanism of TBK1 duplications as non-allelic homologous recombination.