1. ¹Laboratory of Paediatrics and Neurology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
2. ²Department of Endocrinology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
3. ³Department of Epidemiology and Biostatistics, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands

Correspondence: Dr M den Heijer, Department of Endocrinology (471), Radboud University Nijmegen Medical Centre, PO Box 9101, Nijmegen 6500 HB, The Netherlands. Tel: +31 24 3614599; Fax: +31 24 3618809; E-mail: m.denheijer@endo.umcn.nl

Received 19 April 2006; Revised 26 June 2006; Accepted 19 July 2006; Published online 13 September 2006.

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'-upstream region that partially overlapped with the 5'-untranslated region, and several single-nucleotide polymorphisms, all in non-coding regions. We screened subjects for the 9-bp repeat (n=417), as well as the recently reported 19-bp deletion in intron 1 (n=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 (-14.4% [95% confidence interval: -23.5 to -4.5], P=0.006) compared with the wild-type genotype. This may suggest that intracellular folate levels are affected.