Description of SNP SHMT (serine hydroxymethyltransferase): This gene product helps to shift the emphasis of the methylation cycle toward the building blocks needed for new DNA synthesis and way from the processing of homocysteine to methionine. While DNA building blocks are important, mutations which affect the ability to regulate this gene product and interfere with the delicate balance of the methylation cycle may cause accumulations in homocysteine as well as imbalances in other intermediates in the body.