Conversely, in human hyperhomocysteinemia (HHE) due to defective cystathionine beta synthase (CBS), methionine and S-adenosylmethionine are greatly increased but fatty liver occurs in most of these cases (although it is argued that the elevated S-adenosyl homocysteine inhibits the necessary transmethylations). The gene discussed is CBS; the disease is hyperhomocysteinemia.