In contrast to the previous report, which assumed that the 68-bp insertion introduced a premature-termination codon and resulted in a nonfunctional CBS enzyme, we found that the presence of this mutation is not associated with hyperhomocysteinemia.
Severe HHcy (plasma Hcy 210 micromol/L) accelerates spontaneous arthrosclerosis in the CBS(-/-)/apoE(-/-) mice, reduces the concentration of circulating HDL, apoA-I, and large HDL particles, inhibits HDL function, and enhances HDL-C clearance.
Protective effect towards hyperhomocysteinemia was observed with heterozygous (ancestral/insertion) genotype of CBS844ins68 compared to homozygous ancestral type [OR (95% CI); 0.58 (0.34-0.99)].
Stratified analysis by sex found that lower CBS methylation levels were associated with a 2.128-fold increased risk for treatment failure in males with HHcy.
The 31 bp VNTR in the CBS gene is associated with post-methionine load hyperhomocysteinaemia that may predispose individuals to an increased risk of cardiovascular diseases.
Deficiency in cystathionine beta synthase (CBS) enzyme sometimes leads to hyperhomocysteinemia/homocystinuria, conditions often associated with mental retardation (MR).
In humans, severe hyperhomocysteinemia due to genetic alterations in cystathionine beta-synthase (Cbs) or methylenetetrahydrofolate reductase (Mthfr) results in neurological abnormalities and premature death from vascular complications.
This is the first report from Pakistan where novel as well as recurrent CBS mutations causing hyperhomocysteinemia and lens dislocation in three patients from different families are being reported with the predicted effect of the risk allele of the MTHFR SNP in causing hyperhomocysteinemia.
However, it is not known how much of the observed hyperhomocysteinemia in patients with vascular disease is due to heterozygosity for cystathionine-beta-synthase (CbetaS) deficiency, because a clinically useful screening method is unavailable.
This indicates that a search for CBS mutations in patients with severe hyperhomocysteinemia is important to ensure the detection of a possible CBS deficiency, thus enabling treatment.
Mild hyperhomocysteinemia is associated to mutations either in cystathionine beta-synthase (CBS) or in 5,10-methylenetetrahydrofolate reductase (MTHFR) genes.In 1995, Sebastio et al. characterized a 68 bp insertion in cis with the most common CBS mutation (T833C) detected in homocystinuric patients.
In patients with CVT, plasma total homocysteine measurement as part of the etiologic work up may reveal severe hyperhomocysteinemia due to CBS or remethylation defects that require specific treatment and management including perhaps protein-restricted diet and/or vitamin therapy for life.
For example, plasma Hcy-thiolactone was found to be elevated 59-72-fold in human patients with hyperhomocysteinemia secondary to mutations in methylenetetrahydrofolate reductase (MTHFR) or cystathionine beta-synthase (CBS) genes.
Furthermore, we characterized monocyte heterogeneity in Tg-hCBS apoE(-/-) Cbs(-/-) mice and another severe HHcy mouse model (Tg-S466L Cbs(-/-)) with a disease-relevant mutation (Tg-S466L) that lacks hyperlipidemia.
However, folate deficiency, either associated or not associated with the thermolabile mutation of the N(5,10)-methylenetetrahydrofolate reductase, and vitamin B(6) deficiency, perhaps associated with cystathionine beta-synthase defects or with methionine excess, are believed to be major determinants of the increased risk of cardiovascular disease related to hyperhomocysteinemia.
Inherited thrombophilias that have been implicated in venous thromboembolism and poor pregnancy outcome and for which standard tests are generally available are antithrombin III deficiency, the factor V Leiden mutation, prothrombin G20210A mutation and the C677T polymorphism in the methylenetetrahydrofolate reductase system implicated in mild hyperhomocysteinaemia.
One of the plausible reasons for susceptibility of individuals with MTHFRC677T in the studied population to various disorders is the high frequency of hyperhomocysteinemia and vitamin B12 deficiency in the 'healthy population'.
In this study, we investigated the levels of serum folate, vitamin B-12 and Hcy in epileptic patients receiving carbamazepine (CBZ) or valproic acid (VPA) as monotherapy, and we also evaluated the probable contribution of the C677T variant of MTHFR gene in hyperhomocysteinemia.
For example, plasma Hcy-thiolactone was found to be elevated 59-72-fold in human patients with hyperhomocysteinemia secondary to mutations in methylenetetrahydrofolate reductase (MTHFR) or cystathionine beta-synthase (CBS) genes.