The CTH gene encodes for an enzyme that converts cystathionine into cysteine, the second step of the transsulfuration pathway.
CTH acts together with another enzyme,cystathionine-beta-synthase encoded by the CBS gene to convert homocysteine into cysteine, limiting its harmful buildup with this pathway being one of three used to clear homocysteine accumulation. CBS first converts homocysteine into cystathionine, which is then converted into cysteine by the action of CTH.
The T-allele has been associated with an accumulation of homocysteine. Vitamin B6 is an important nutrient cofactor to support proper CTH function.