MTHFR and Schnyder corneal dystrophy: With regards to MTHFR TT, the pooled prevalence of this genotype was low and relatively similar between SCD and controls, and even if the prevalence of the other MTHFR 1298CC genotype was double of that of controls, the contribution of both genes to the clinical manifestations of SCD remains dubious; having excluded a study that mixed adult and paediatric patients [49], the pooled prevalence of MTHFR TT in patients with ischemic stroke was higher than non-stroke controls, but still at a relatively low 5.9%.