The MTR A2756G polymorphism is associated with an increase of plasma homocysteine concentration in Brazilian individuals with Down syndrome. 
Individuals with Down syndrome (DS) present decreased homocysteine (Hcy) concentration, reflecting a functional folate deficiency secondary to overexpression of the cystathionine ss-synthase gene.  Since plasma Hcy may be influenced by genetic polymorphisms, we evaluated the influence of C677T and A1298C polymorphisms in the methylenetetrahydrofolate reductase gene (MTHFR), of A2756G polymorphism in the methionine synthase gene (MTR), and of A80G polymorphism in the reduced folate carrier 1 gene on Hcy concentrations in Brazilian DS patients.  Fifty-six individuals with free trisomy 21 were included in the study.  Plasma Hcy concentrations were measured by liquid chromatography_tandem mass spectrometry with linear regression coefficient r(2) = 0.9996, average recovery between 92.3 to 108.3% and quantification limits of 1.0 micromol/L. Hcy concentrations >15 micromol/L were considered to characterize hyperhomocystinemia.  Genotyping for the polymorphisms was carried out by polymerase chain reaction followed by enzyme digestion and allele-specific polymerase chain reaction.  The mean Hcy concentration was 5.2 +/- 3.3 micromol/L. There was no correlation between Hcy concentrations and age, gender or MTHFR C677T, A1298C and reduced folate carrier 1 A80G genotype.  However, Hcy concentrations were significantly increased in the MTR 2756AG heterozygous genotype compared to the MTR 2756AA wild-type genotype.  The present results suggest that the heterozygous genotype MTR 2756AG is associated with the increase in plasma Hcy concentrations in this group of Brazilian patients with DS.