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Cystathionine-gamma-ligase (CTH) is an enzyme which converts cystathionine into cysteine, the second step of the transsulfuration pathway which is encoded for by the CTH gene 1.

CTH acts together with another enzyme, cystathionine-beta-synthase (CBS) 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 2. While there are several SNPs of interest in CBS only one has been described for CTH and it appears to be of less importance.


Science Grade
Gastrointestinal Health
rsID Number Major Allele Minor Allele Minor Allele Frequency (%) Major Amino Acid Minor Amino Acid
rs1021737 g t 20 Ser Ile

Risk Description

The risk ‘T’ allele of G1208T in the CTH gene has been associated with an accumulation of homocysteine specifically in an ethnic Chinese population 3. However, the authors do not describe a mechanism, although reduced enzyme activity seems the most likely cause, nor have any other groups replicated these findings.

Direct Nutrients:*

Ingredient Active Ingredient Effect
Vitamin B6 Pyridoxal phosphate

As with CBS vitamin B6 is the co-factor for CTH and is required for its activity. Although it is unclear if the risk ‘T’ allele of G1208T is associated with reduced enzyme activity, ensuring adequate levels of vitamin B6 should maintain enzyme function. An excellent response for CBS SNPs has been observed but not data for CTH has been generated 4.

Discuss this information with your doctor before taking any course of action.


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