Molecular genetic analysis of the human dihydrofolate reductase gene: relation with plasma total homocysteine, serum and red blood cell folate levels

Abstract

Disturbances in folate metabolism may increase the risk of certain malignancies, congenital defects and cardiovascular diseases. The gene dihydrofolate reductase (DHFR) is primarily involved in the reduction of dihydrofolate, generated during thymidylate synthesis, to tetrahydrofolate in order to maintain adequate amounts of folate for DNA synthesis and homocysteine remethylation. In order to reveal possible variation that may affect plasma total homocysteine (tHcy), serum folate and red blood cell (RBC) folate levels, we sequenced the DHFR coding region as well as the intron -exon boundaries and DHFR flanking regions from 20 Caucasian individuals. We identified a 9-bp repeat in the 5 0 -upstream region that partially overlapped with the 5 0 -untranslated region, and several single-nucleotide polymorphisms, all in non-coding regions. We screened subjects for the 9-bp repeat (n ¼ 417), as well as the recently reported 19-bp deletion in intron 1 (n ¼ 330), and assessed their associations with plasma tHcy, serum and RBC folate levels. The 19-bp del/del genotype was associated with a lower plasma tHcy (À14.4% [95% confidence interval: À23.5 to À4.5], P ¼ 0.006) compared with the wild-type genotype. This may suggest that intracellular folate levels are affected.

Survival and risk of relapse of acute lymphoblastic leukemia in a Mexican population is affected by dihydrofolate reductase gene polymorphisms

“…The C829T polymorphism has been studied in other disorders that involve the metabolic pathway of folate. However, it was not identified in non-Japanese American, Caucasian or Israeli populations (21)(22)(23), suggesting that the C829T polymorphism was found more frequently in patients with ALL than in other disorders in which the activity enzymatic of DHFR is involved.…”

Influence of Reduced Folate Carrier and Dihydrofolate Reductase Genes on Methotrexate-Induced Cytotoxicity

“…A 19-bp deletion in the highly conserved intron and only a few variant such as a 9-bp repeat in exon 1 of the DNA repair gene mutS homolog3 were detected in Japanese subjects (1,21,22). The DHFR gene is the most important target for determining the activity of MTX, and the concentration of MTX required to achieve effective inhibition of DHFR enzymatic activity is strictly dependent on the intracellular levels of this enzyme.…”

Investigation of inter-individual variability of the one-carbon folate pathway: a bioinformatic and genetic review

“…The 19-bp deletion polymorphism in intron 1 in the DHFR gene has been associated with a number of diseases 41 (Table 3). Individuals homozygous for the deletion (À/À) have lower mean plasma total homocysteine than those homozygous for the insertion ( þ / þ ), 40 with the (À/À) individuals also having been shown to have 4.8-fold greater DHFR mRNA expression in lymphocytes compared with ( þ / þ ) carriers. 42 The 5 0 -upstream 9-bp repeat polymorphism (homozygous 6R carriers) 43 and 3 0 -UTR SNP (rs34764978) (C/T and T/T carriers) 44 have also been associated with enhanced mRNA expression.…”

“…The importance of the DHFR protein is perhaps illustrated by the finding that the coding region is highly conserved with no allelic variants having been identified. 40 There are three non-coding polymorphisms (in the 5 0 upstream region, intron 1 and 3 0 -UTR) that have been the subject of a number of association studies (Table 3). The 19-bp deletion polymorphism in intron 1 in the DHFR gene has been associated with a number of diseases 41 (Table 3).…”