Choline metabolism, phosphatidylcholine and sphingomyelin synthesis, and the role of betaine and folate in one-carbon metabolism. BHMT, betaine homocysteine S-methyltransferase; CDP-Cho, cytidinediphosphocholine; CMP, cytidinemonophosphate; CTP, cytidinetriphosphate, DAG, diacylglycerol; DMG, dimethylglycine; HCY, homocysteine; MET, methionine; MTHFR, methylenetetrahydrofolate reductase; PC, phosphocholine; PtdCho, phosphatidylcholine; PtdEth, phosphatidylethanolamine; SAH, S-adenosylhomocysteine; SAM, S-adenosylmethionine; SM, sphingomyelin; THF, tetrahydrofolate.