Elevated total plasma homocysteine (tHcy) is an established risk factor for the development of vascular disease and neural tube defects. Total homocysteine levels can be lowered by folic acid supplements but individual response is highly variable. In this case-control study, involving 142 coronary artery disease (CAD) patients and 102 controls, we have typed six genetic polymorphisms in three homocysteine metabolizing genes and examined their relationship to the incidence of CAD, tHcy levels, and lowering of tHcy levels in response to folic acid supplementation. We found that two single nucleotide polymorphisms in the cystathionine beta synthase (CBS) gene, 699C --> T and 1080T --> C, are associated with decreased risk of CAD and increased responsiveness to the tHcy lowering effects of folic acid. Individuals homozygous for 699T were significantly underrepresented in CAD patients as compared to controls (4.9% vs 17.3%, P = 0.0015), as were individuals homozygous for the 1080C (29.6% vs 44.2%, P = 0.018). Additionally, 699T and 1080C homozygous individuals were the most responsive to folate supplementation. 699T homozygotes lowered tHcy levels 13.6% on average, compared to 4.8% lowering in 699C homozygotes (P = 0.009), while 1080C homozygotes lowered 12.9% compared to just 2.7% for 1080T homozygotes (P = 0.005). The two polymorphisms in CBS are third codon changes and would not be predicted to affect the underlying protein. However, there is strong linkage disequilibrium between these two positions, suggesting that they may also be linked to other as yet unidentified polymorphisms within the CBS gene. These observations suggest that specific CBS alleles are a risk factor for the development of vascular disease and that genetic information could be predictive of individual response to folic acid supplementation.
Copyright 2000 Academic Press.