Determinants of plasma homocysteine

Hyperhomocysteinemia in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)

OBJECTIVE

To determine whether patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) had evidence of increased homocysteine levels compared with non-CADASIL patients with ischemic stroke or transient ischemic attack.

PATIENTS AND METHODS

We compared fasting plasma homocysteine levels and levels 6 hours after oral loading with methionine, 100 mg/kg, in non-CADASIL patients with ischemic stroke or transient ischemic attack and in patients with CADASIL. Prechallenge, postchallenge, and change in homocysteine levels between the 2 groups were compared with use of the Wilcoxon rank sum test.

RESULTS

CADASIL and non-CADASIL groups were similar in age (mean, 48.8 vs. 46.5 years, respectively; 2-tailed t test, P=.56) and sex (men, 86% vs 59%; Fisher exact test, P=.12). The 59 patients in the CADASIL group had higher median plasma homocysteine levels compared with the 14 patients in the non-CADASIL group, both in the fasting state (12.0 vs 9.0 micromol/L; P=.03) and after methionine challenge (51.0 vs 34.0 micromol/L; P=.007). Median difference between homocysteine levels before and after methionine challenge was greater in the CADASIL group than in the non-CADASIL group (34.5 vs. 24.0 micromol/ L; P = .02).

CONCLUSION

Our findings raise the possibility that increased homocysteine levels or abnormalities of homocysteine metabolism may have a role in the pathogenesis of CADASIL.

Betaine-homocysteine methyltransferase (BHMT): genomic sequencing and relevance to hyperhomocysteinemia and vascular disease in humans

Elevated homocysteine levels have been associated with arteriosclerosis and thrombosis. Hyperhomocysteinemia is caused by altered functioning of enzymes of its metabolism due to either inherited or acquired factors. Betaine-homocysteine methyltransferase (BHMT) serves, next to methionine synthase, as a facilitator of methyl group donation for remethylation of homocysteine into methionine, and reduced functioning of BHMT could theoretically result in elevated homocysteine levels. Recently, the genomic sequence of the BHMT gene was published. Mutation analysis may reveal mutations of the BHMT gene that could lead to hyperhomocysteinemia. In the present study we performed genomic sequencing of the BHMT gene of 16 vascular patients with hyperhomocysteinemia and detected three mutations in the coding region of this gene. The first was an amino acid substitution of glycine to serine (G199S), which was found only in the heterozygous state. The second mutation was a substitution of glutamine to arginine (Q239R), and the last mutation was an amino acid substitution of glutamine to histidine (Q406H). The latter was also found only in the heterozygous state. The relevance of these mutations was tested in a study group, which consists of 190 cases with vascular disease and 601 controls. The influence of these three mutations on homocysteine levels was investigated. None of the three mutations led to significantly changed homocysteine levels. In addition, no differences in genotype distribution between cases and controls were found. So far, our results provide no evidence for a role of defective BHMT functioning in hyperhomocysteinemia or subsequently in vascular disease.