title: Human mutations in methylenetetrahydrofolate dehydrogenase 1 impair nuclear de novo thymidylate biosynthesis.
abstract: An inborn error of metabolism associated with mutations in the human methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) gene has been identified. The proband presented with SCID, megaloblastic anemia, and neurologic abnormalities, but the causal metabolic impairment is unknown. SCID has been associated with impaired purine nucleotide metabolism, whereas megaloblastic anemia has been associated with impaired de novo thymidylate (dTMP) biosynthesis. MTHFD1 functions to condense formate with tetrahydrofolate and serves as the primary entry point of single carbons into folate-dependent one-carbon metabolism in the cytosol. In this study, we examined the impact of MTHFD1 loss of function on folate-dependent purine, dTMP, and methionine biosynthesis in fibroblasts from the proband with MTHFD1 deficiency. The flux of formate incorporation into methionine and dTMP was decreased by 90% and 50%, respectively, whereas formate flux through de novo purine biosynthesis was unaffected. Patient fibroblasts exhibited enriched MTHFD1 in the nucleus, elevated uracil in DNA, lower rates of de novo dTMP synthesis, and increased salvage pathway dTMP biosynthesis relative to control fibroblasts. These results provide evidence that impaired nuclear de novo dTMP biosynthesis can lead to both megaloblastic anemia and SCID in MTHFD1 deficiency.
authors.affiliation: Division of Nutritional Sciences and.
authors.forename: Martha S
authors.initials: MS
authors.lastname: Field
authors.affiliation: Division of Nutritional Sciences and.
authors.forename: Elena
authors.initials: E
authors.lastname: Kamynina
authors.affiliation: Department of Human Genetics, McGill University, Montreal, Quebec, Canada H3A 1B1; and Department of Medical Genetics, McGill University Health Centre, Montreal, Quebec, Canada H3G 1A4.
authors.forename: David
authors.initials: D
authors.lastname: Watkins
authors.affiliation: Department of Human Genetics, McGill University, Montreal, Quebec, Canada H3A 1B1; and Department of Medical Genetics, McGill University Health Centre, Montreal, Quebec, Canada H3G 1A4.
authors.forename: David S
authors.initials: DS
authors.lastname: Rosenblatt
authors.affiliation: Division of Nutritional Sciences and Graduate Field of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY 14853; PJS13@cornell.edu.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Stover
mesh_terms: D019943:Amino Acid Substitution; D000749:Anemia, Megaloblastic / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D018389:Codon, Nonsense; D004249:DNA Damage; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D053858:Metabolic Networks and Pathways; D008754:Methylenetetrahydrofolate Dehydrogenase (NADP) / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics*; D015778:Minor Histocompatibility Antigens; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010641:Phenotype; D017354:Point Mutation; D016511:Severe Combined Immunodeficiency / Q000235:genetics / Q000378:metabolism; D013938:Thymidine Monophosphate / Q000096:biosynthesis*
chemical_list: D018389:Codon, Nonsense; D015778:Minor Histocompatibility Antigens; D050505:Mutant Proteins; D013938:Thymidine Monophosphate; C539735:MTHFD1 protein, human; D008754:Methylenetetrahydrofolate Dehydrogenase (NADP)
keywords: MTHFD1; SCID; folate; megaloblastic anemia; thymidylate