Characterization of mutations in severe methylenetetrahydrofolate reductase deficiency reveals an FAD-responsive mutation

• Published in: Human mutation 2003-05, Vol.21 (5), p.509-520
• Main Authors: Sibani, Sahar, Leclerc, Daniel, Weisberg, Ilan S., O'Ferrall, Erin, Watkins, David, Artigas, Carmen, Rosenblatt, David S., Rozen, Rima
• Format: Article
• Language: English
• Subjects: Age of Onset; DNA - chemistry; DNA - genetics; DNA Mutational Analysis; Enzyme Stability - drug effects; Enzyme Stability - genetics; Family Health; Female; Flavin-Adenine Dinucleotide - pharmacology; folate; homocysteine; homocystinuria; Homocystinuria - enzymology; Homocystinuria - genetics; Humans; Male; methylenetetrahydrofolate reductase; Methylenetetrahydrofolate Reductase (NADPH2); MTHFR; Mutation; mutations; Oxidoreductases Acting on CH-NH Group Donors - deficiency; Oxidoreductases Acting on CH-NH Group Donors - genetics; Oxidoreductases Acting on CH-NH Group Donors - metabolism; Pedigree
• ISSN: 1059-7794; 1098-1004
• DOI: 10.1002/humu.10193

Methylenetetrahydrofolate reductase (MTHFR) synthesizes 5‐methyltetrahydrofolate, a major methyl donor for homocysteine remethylation to methionine. Severe MTHFR deficiency results in marked hyperhomocysteinemia and homocystinuria. Patients display developmental delay and a variety of neurological and vascular symptoms. Cloning of the human cDNA and gene has enabled the identification of 29 rare mutations in homocystinuric patients and two common variants [677C>T (A222V) and 1298A>C (E429A)] with mild enzymatic deficiency. Homozygosity for 677C>T or combined heterozygosity for both polymorphisms is associated with mild hyperhomocysteinemia. In this communication, we describe four novel mutations in patients with homocystinuria: two missense mutations (471C>G, I153M; 1025T>C, M338T), a nonsense mutation (1274G>A, W421X), and a 2‐bp deletion (1553delAG). We expressed the 1025T>C mutation as well as two previously reported amino acid substitutions [983A>G (N324S) and 1027T>G (W339G)] and observed decreased enzyme activity at 10%, 36%, and 21% of control levels, respectively, with little or no effect on affinity for 5‐methyltetrahydrofolate. One of these mutations, 983A>G (N324S), showed flavin adenine dinucleotide (FAD) responsiveness in vitro. Expression of these mutations in cis with the 677C>T polymorphism, as observed in the patients, resulted in an additional 50% decrease in enzyme activity. This report brings the total to 33 severe mutations identified in patients with severe MTHFR deficiency. Hum Mutat 21:509–520, 2003. © 2003 Wiley‐Liss, Inc.