MOLECULAR-GENETIC ANALYSIS OF THE GENE ENCODING THE TRIFUNCTIONAL ENZYME MTHFD (METHYLENETETRAHYDROFOLATE-DEHYDROGENASE METHENYLTETRAHYDROFOLATE-CYCLOHYDROLASE, FORMYLTETRAHYDROFOLATE SYNTHETASE) IN PATIENTS WITH NEURAL-TUBE DEFECTS

It is now well recognized that periconceptional folic acid or folic ac id containing multivitamin supplementation reduces the risk of neural tube defects (NTDs). Recently we were able to show that homozygosity f or a thermolabile variant of the enzyme methylenetetrahydrofolate redu ctase is associated with an increased risk for spina bifida in patient s recruited from the Dutch population. However, this genetic risk fact or could not account for all folic acid preventable NTDs. In an attemp t to identify additional folate related enzymes that contribute to NTD etiology we now studied the methylenetetrahydrofolate dehydrogenase g ene on chromosome 14q24 which encodes a single protein with three cata lytic properties important in the folate metabolism. The cDNA sequence of 38 familial and 79 sporadic patients was screened for the presence of mutations by single strand conformation polymorphism (SSCP) analys is followed by sequencing. Two amino acid substitutions were identifie d. The first one (R293H) was detected in a patient with familial spina bifida and not in 300 control individuals. The mutation was inherited from the unaffected maternal grandmother and was also present in two younger brothers of the index patient, one of them displaying spina bi fida occulta and the other being unaffected. The second change turned out to be an amino acid polymorphism (R653Q) that was present in both patients and controls with similar frequencies. Our results so far pro vide no evidence for a major role of the methylenetetrahydrofolate-deh ydrogenase (MTHFD) gene in NTD etiology. However. the identification o f a mutation in one family suggests that this gene can act as a risk f actor for human NTD.