Thermolabile MTHFR genotype and retinal vascular occlusive disease

Background-Raised levels of total plasma homocysteine (tHcy) are associated with an increased risk of retinal vascular occlusive disease. A thermolabi le form of a pivotal enzyme in homocysteine metabolism, methylenetetrahydro folate reductase (MTHFR), has been associated with vascular occlusive disea se and raised tHcy levels. The relation between thermolabile MTHFR genotype , tHcy, and retinal vascular occlusive disease has not been determined. Methods-A retrospective case-control study involving hospital based control s and cases with retinal vascular occlusions in whom tHcy levels had been d etermined was undertaken. Genotyping for the MTHFR 677 C-T mutation that sp ecifies the thermolabile form of the enzyme was performed by established me thods in all subjects. The relation between homozygosity for thermolabile M THFR genotype (TT), raised tHcy levels, and risk of retinal vascular occlus ive disease was examined. Results-87 cases of retinal vascular occlusive disease (mean age 68.7 years ) comprising 26 cases of retinal artery occlusion and 61 of retinal vein oc clusion were compared with 87 controls (mean age 70.2 years). The TT genoty pe did not confer a significantly increased risk of retinal vascular occlus ive disease. The mean tHcy level was significantly higher in the cases than in the controls (p<0.0001). Overall, and in both the cases and controls, t he frequency of the TT genotype was higher in those with normal tHcy levels than in those with increased levels of tHcy. However, the TT genotype did not significantly alter the risk of increased tHcy levels in these patients . Conclusions-The TT genotype is not associated with an increased risk of ret inal vascular occlusive disease or increased tHcy levels in this group of e lderly patients. In older patients, nutritional rather than genetic factors may be more important in increasing tHcy levels, a known risk factor for r etinal vascular occlusive disease.