Primary open angle glaucoma due to T377M MYOC: Population mapping of a Greek founder mutation in Northwestern Greece

George Kitsos¹, Zacharias Petrou², Maria Grigoriadou³, John R Samples⁴, Alex W Hewitt⁵, Haris Kokotas³, Aglaia Giannoulia-Karantana³, David A Mackey⁶, Mary K Wirtz⁴, Marilita Moschou⁷, John PA Ioannidis⁸, Michael B Petersen³

¹Department of Ophthalmology, University of Ioannina, School of Medicine, Ioannina, Greece; ²Department of Ophthalmology, General Hospital of Ioannina “G Chatzikosta”, Ioannina, Greece; ³Department of Genetics, Institute of Child Health, Athens, Greece; ⁴Department of Ophthalmology, Casey Eye Institute-OHS U, Portland, OR; ⁵Department of Ophthalmology, Flinders University, Adelaide, Australia; ⁶Center for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia; ⁷Department of Ophthalmology, University of Athens, School of Medicine, Athens, Greece; ⁸Department Hygiene and Epidemiology, University of Ioannina, School of Medicine, Ioannina, Greece

Background: Mutations in the MYOC gene have been shown to explain 5% of unrelated primary open angle glaucoma (POAG) in different populations. In particular, the T377M MYOC mutation has arisen at least three separate times in history, in Great Britain, India, and Greece. The purpose of this study is to investigate the distribution of the mutation among different population groups in the northwestern region of Greece.

Materials and methods: We explored the distribution of the “Greek” T377M founder mutation in the Epirus region in Northwestern Greece, which could be its origin. Genotyping was performed in POAG cases and controls by PCR amplification of the MYOC gene, followed by digestion with restriction enzyme. Statistical analyses were performed by an exact test, the Kaplan–Meier method and the t-test.

Results: In the isolated Chrysovitsa village in the Pindus Mountains, a large POAG family demonstrated the T377M mutation in 20 of 66 family members while no controls from the Epirus region (n = 124) carried this mutation (P < 0.001). Among other POAG cases from Epirus, 2 out of 14 familial cases and 1 out of 80 sporadic cases showed the mutation (P = 0.057). The probability of POAG diagnosis with advancing age among mutation carriers was 23% at age 40, and reached 100% at age 75. POAG patients with the T377M mutation were diagnosed at a mean age of 51 years (SD ± 13.9), which is younger than the sporadic or familial POAG cases: 63.1 (SD ± 11) and 66.8 (SD ± 9.8) years, respectively.

Conclusions: The T377M mutation was found in high proportion in members of the Chrysovitsa family (30.3%), in lower proportion in familial POAG cases (14.2%) and seems rare in sporadic POAG cases (1.2%), while no controls (0%) from the Epirus region carried the mutation. Historical and geographical data may explain the distribution of this mutation within Greece and worldwide.

Keywords: primary open angle glaucoma, GLC1C, myocilin, MYOC, founder mutation