Hyperhomocysteinemia is related to homocysteinemia and homocystinuria due to deficiency of n -methylenetetrahydrofolate reductase activity. An important gene associated with Hyperhomocysteinemia is H19 (H19 Imprinted Maternally Expressed Transcript), and among its related pathways/superpathways are Metabolism and Response to elevated platelet cytosolic Ca2+. The drugs Hydrochlorothiazide and Amlodipine have been mentioned in the context of this disorder. Affiliated tissues include endothelial and kidney, and related phenotypes are homeostasis/metabolism and liver/biliary system