Description of SNP AHCY 1,2,19 (S adenosylhomocysteine hydrolase): AHCY is the enzyme that converts s adenosyl homocysteine (SAH) to adenosine and homocysteine. Decreased AHCY activity should lead to lower levels of homocysteine. Studies using animals with no CBS function suggests that the relationship between CBS enzyme activity, homocysteine levels and SAH and SAMe levels may not be as simple or predictable as one might expect from pathway diagrams. In addition, both SAH and SAMe have been found to affect CBS activity and SAH is known to inhibit methyltrasferase reactions. Also the level of homocysteine affects SAH levels such that higher levels of homocysteine can increase SAH. Clearly, the relationship between these intermediates appears to be complex. (PNAS 2008, 103:17; Theorectic Biology and Medical Modelling 2008, 5:8; JBC 2002, 277:41; Jnutrition 2002,132) It may be especially important for those with AHCY mutations to monitor amino acid levels in order to balance the effects of AHCY mutations, CBS up regulations and other methylation cycle mutation on the system.