Figure 1. Homocysteine metabolic pathways. Products of the enzymatic pathways are shown in rectangles, co-factors are shown in circles, and enzymes are in text. The genes coding for the enzymes included in this study are shown as underlined text. Abbreviations: B12, vitamin B12; BHMT, betaine-homocysteine methyltransferase; CBS, cystathionine beta synthase; DHF, dihydrofolate; DHFR, dihydrofolate reductase; dTMP, thymidine monophosphate; dUMP, uridine monophosphate; FAD, flavin adenine dinucleotide; GLY, glycine; MTHFD1, trifunctional methylenetetrahydrofolate dehydrogenase, cyclohydrolase, synthase; MTHFR, methylenetetrahydrofolate reductase; MTR, 5-methyltetrahydrofolate-homocysteine methyltransferase; MTRR, 5-methyltetrahydrofolate-homocysteine methyltransferase reductase; MT, methyl transferase; SAH, S-adenosylhomocysteine hydrolase; SER, serine; THF, tetrahydrofolate; TS, thymidylate synthase; 5-CH3-THF, 5-methyl tetrahydrofolate; 5,10-CH2=THF, methylene tetrahydrofolate; 5,10=CH2-THF, methenyl tetrahydrofolate; 10-CHO-THF, 10-formyl tetrahydrofolate.