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Primary open angle glaucomas (POAGs) affect around 1–2% of people and are a major cause of blindness in Western countries. Some patients with POAG have normal tension glaucoma (NTG, intraocular pressure <21 mm Hg) and it is not clear whether these patients have a different pathology. Genetic factors are important in POAG but the genetics is complex. The OPTINEURIN (OPTN) gene on the short arm of chromosome 10 (10p14) has been implicated in NTG and the M98K variant is more common in POAG patients. Now a study in France and Morocco has shown that this variant is associated with lower initial intraocular pressure in patients with POAG.
The study included 237 patients with POAG and 110 controls (healthy spouses) in France and 56 patients and 60 general population controls in Morocco. The M98K variant of the OPTN gene was found in 4.6% of cases and 4.5% of controls in France and in 10.7% of cases and 8.3% of controls in Morocco. There was no significant difference between cases and controls but the M98K variant was twice as frequent in Morocco. The variant was associated with normal or moderately increased pressure glaucoma. Initial intraocular pressure (before treatment) was lower in patients with the variant allele (mean pressure 25.9 mm Hg (M98K positive) v 32.3 mm Hg (M98K negative) in the French groups (highly significant), and 32.3 v 37.3 mm Hg in Moroccan group (not significant)). For the pooled populations mean initial intraocular pressure was highly significantly lower (28.2 v 33.4 mm Hg) in M98K positive patients.
The M98K variant of the OPTN gene does not increase the risk of POAG but it is associated with lower initial intraocular pressure in patients with POAG.