Abstract
5-Methyltetrahydrofolate, the major form of folate in plasma, is a carbon donor for the remethylation of homocysteine to methionine. This form of folate is generated from 5,10-methylenetetrahydrofolate through the action of 5,10-methylenetetrahydrofolate reductase (MTHFR), a cytosolic flavoprotein. Patients with an autosomal recessive severe deficiency of MTHFR have homocystinuria and a wide range of neurological and vascular disturbances. We have recently described the isolation of a cDNA for MTHFR and the identification of two mutations in patients with severe MTHFR deficiency. We report here the characterization of seven novel mutations in this gene: six missense mutations and a 5' splice-site defect that activates a cryptic splice site in the coding sequence. We also present a preliminary analysis of the relationship between genotype and phenotype for all nine mutations identified thus far in this gene. A nonsense mutation and two missense mutations (proline to leucine and threonine to methionine) in the homozygous state are associated with extremely low activity (0%-3%) and onset of symptoms within the 1st year of age. Other missense mutations (arginine to cysteine and arginine to glutamine) are associated with higher enzyme activity and later onset of symptoms.
Full text
PDF
Images in this article
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Ahearn J. M., Jr, Bartolomei M. S., West M. L., Cisek L. J., Corden J. L. Cloning and sequence analysis of the mouse genomic locus encoding the largest subunit of RNA polymerase II. J Biol Chem. 1987 Aug 5;262(22):10695–10705. [PubMed] [Google Scholar]
- Beckman D. R., Hoganson G., Berlow S., Gilbert E. F. Pathological findings in 5,10-methylene tetrahydrofolate reductase deficiency. Birth Defects Orig Artic Ser. 1987;23(1):47–64. [PubMed] [Google Scholar]
- Broderick T. P., Schaff D. A., Bertino A. M., Dush M. K., Tischfield J. A., Stambrook P. J. Comparative anatomy of the human APRT gene and enzyme: nucleotide sequence divergence and conservation of a nonrandom CpG dinucleotide arrangement. Proc Natl Acad Sci U S A. 1987 May;84(10):3349–3353. doi: 10.1073/pnas.84.10.3349. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Davies J. F., 2nd, Delcamp T. J., Prendergast N. J., Ashford V. A., Freisheim J. H., Kraut J. Crystal structures of recombinant human dihydrofolate reductase complexed with folate and 5-deazafolate. Biochemistry. 1990 Oct 9;29(40):9467–9479. doi: 10.1021/bi00492a021. [DOI] [PubMed] [Google Scholar]
- Degen S. J., Davie E. W. Nucleotide sequence of the gene for human prothrombin. Biochemistry. 1987 Sep 22;26(19):6165–6177. doi: 10.1021/bi00393a033. [DOI] [PubMed] [Google Scholar]
- Freeman J. M., Finkelstein J. D., Mudd S. H. Folate-responsive homocystinuria and "schizophrenia". A defect in methylation due to deficient 5,10-methylenetetrahydrofolate reductase activity. N Engl J Med. 1975 Mar 6;292(10):491–496. doi: 10.1056/NEJM197503062921001. [DOI] [PubMed] [Google Scholar]
- Goyette P., Sumner J. S., Milos R., Duncan A. M., Rosenblatt D. S., Matthews R. G., Rozen R. Human methylenetetrahydrofolate reductase: isolation of cDNA, mapping and mutation identification. Nat Genet. 1994 Jun;7(2):195–200. doi: 10.1038/ng0694-195. [DOI] [PubMed] [Google Scholar]
- Harpey J. P., Rosenblatt D. S., Cooper B. A., Le Moël G., Roy C., Lafourcade J. Homocystinuria caused by 5,10-methylenetetrahydrofolate reductase deficiency: a case in an infant responding to methionine, folinic acid, pyridoxine, and vitamin B12 therapy. J Pediatr. 1981 Feb;98(2):275–278. doi: 10.1016/s0022-3476(81)80660-9. [DOI] [PubMed] [Google Scholar]
- John S. W., Rozen R., Laframboise R., Laberge C., Scriver C. R. Novel PKU mutation on haplotype 2 in French-Canadians. Am J Hum Genet. 1989 Dec;45(6):905–909. [PMC free article] [PubMed] [Google Scholar]
- Kang S. S., Wong P. W., Susmano A., Sora J., Norusis M., Ruggie N. Thermolabile methylenetetrahydrofolate reductase: an inherited risk factor for coronary artery disease. Am J Hum Genet. 1991 Mar;48(3):536–545. [PMC free article] [PubMed] [Google Scholar]
- Kim J. J., Wang M., Paschke R. Crystal structures of medium-chain acyl-CoA dehydrogenase from pig liver mitochondria with and without substrate. Proc Natl Acad Sci U S A. 1993 Aug 15;90(16):7523–7527. doi: 10.1073/pnas.90.16.7523. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mudd S. H., Uhlendorf B. W., Freeman J. M., Finkelstein J. D., Shih V. E. Homocystinuria associated with decreased methylenetetrahydrofolate reductase activity. Biochem Biophys Res Commun. 1972 Jan 31;46(2):905–912. doi: 10.1016/s0006-291x(72)80227-4. [DOI] [PubMed] [Google Scholar]
- Rosenblatt D. S., Erbe R. W. Methylenetetrahydrofolate reductase in cultured human cells. II. Genetic and biochemical studies of methylenetetrahydrofolate reductase deficiency. Pediatr Res. 1977 Nov;11(11):1141–1143. doi: 10.1203/00006450-197711000-00005. [DOI] [PubMed] [Google Scholar]
- Rosenblatt D. S., Lue-Shing H., Arzoumanian A., Low-Nang L., Matiaszuk N. Methylenetetrahydrofolate reductase (MR) deficiency: thermolability of residual MR activity, methionine synthase activity, and methylcobalamin levels in cultured fibroblasts. Biochem Med Metab Biol. 1992 Jun;47(3):221–225. doi: 10.1016/0885-4505(92)90029-x. [DOI] [PubMed] [Google Scholar]
- Senapathy P., Shapiro M. B., Harris N. L. Splice junctions, branch point sites, and exons: sequence statistics, identification, and applications to genome project. Methods Enzymol. 1990;183:252–278. doi: 10.1016/0076-6879(90)83018-5. [DOI] [PubMed] [Google Scholar]
- Volz K. W., Matthews D. A., Alden R. A., Freer S. T., Hansch C., Kaufman B. T., Kraut J. Crystal structure of avian dihydrofolate reductase containing phenyltriazine and NADPH. J Biol Chem. 1982 Mar 10;257(5):2528–2536. [PubMed] [Google Scholar]