MTHFD1 is a trifunctional cytoplasmic enzyme catalyzing the interconversion of three one-carbon-substituted tetrahydrofolate derivatives: 5,10-methylene-THF, 5,10-methenyl-THF, and 10-formyl-THF 1. These interconversions are essential for nucleotide and amino acid biosynthesis, with 10-formyl-THF required for purine synthesis and 5,10-methylene-THF utilized in serine and methionine biosynthesis 2. MTHFD1 functions as a critical metabolic hub in cancer progression. In melanoma, MTHFD1 supports NADPH generation within the folate pathway, enabling metastatic cells to withstand oxidative stress during dissemination; MTHFD1 knockdown inhibits distant metastasis without affecting primary tumor growth 3. Similarly, in MYCN-amplified neuroblastoma, MTHFD1 maintains NADPH/NADP+ and GSH/GSSG redox homeostasis; MTHFD1 knockdown increases reactive oxygen species and triggers apoptosis 4. In pancreatic cancer, MTHFD1 activation via decrotonylation at specific lysine residues promotes ferroptosis resistance and tumor progression 5. MTHFD1 polymorphisms show significant associations with congenital heart disease (CHD). Maternal MTHFD1 variants at rs1950902, rs2236222, rs1256142, and rs11849530 increase CHD risk, with interaction effects observed with maternal smoking exposure 6. Meta-analysis confirms fetal MTHFD1 G1958A polymorphism increases Tetralogy of Fallot risk, while maternal polymorphism increases overall CHD risk, particularly in Caucasian populations 7. However, the MTHFD1 1958G>A variant alone shows no association with non-syndromic cleft palate 8.