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Characterization of mutations in severe methylenetetrahydrofolate reductase deficiency reveals an FAD‐responsive mutation
Author(s) -
Sibani Sahar,
Leclerc Daniel,
Weisberg Ilan S.,
O'Ferrall Erin,
Watkins David,
Artigas Carmen,
Rosenblatt David S.,
Rozen Rima
Publication year - 2003
Publication title -
human mutation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 162
eISSN - 1098-1004
pISSN - 1059-7794
DOI - 10.1002/humu.10193
Subject(s) - methylenetetrahydrofolate reductase , hyperhomocysteinemia , missense mutation , biology , homocystinuria , genetics , reductase , compound heterozygosity , nonsense mutation , mutation , flavin adenine dinucleotide , methionine , homocysteine , microbiology and biotechnology , cystathionine beta synthase , biochemistry , enzyme , allele , gene , amino acid , cofactor
Abstract 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.