Synchronous gastric and sebaceous cancers, a rare manifestation of MLH1-related Muir-Torre syndrome.

Muir-Torre syndrome (MTS), a rare variant of the hereditary non polyposis colorectal cancer syndrome, is an autosomal dominant genodermatosis characterised by coincidence of sebaceous gland neoplasms (sebaceous adenoma, epithelioma, or carcinoma) and at least one internal malignancy. The underlying cause of MTS is a germline mutation in DNA mismatch repair genes MSH2, MLH1 and MSH6. We report the case of a 52-year-old caucasian woman with the development of metachronous colon cancer at the age of 38 years, uterine cancer at the age of 43 years, and unique occurrence of synchronous gastric and sebaceous carcinomas related to germline point mutation c. 2194A>T in the last exon of MLH1 gene, resulting in truncated protein in C-terminal region p. Lys732X due to premature stop codon. This mutation, not previously reported in MTS, disrupts the function of MutL complexes presumably by preventing the interaction with PMS1/PMS2 and impairing the endonuclease active site. This case points out the importance of sebaceous neoplasia, especially sebaceous adenocarcinoma, as cutaneous markers of MTS for timely implementation of cancer screening programs.

Rare allelic variants determine folate status in an unsupplemented European population.

The role of folates as coenzymes in 1-carbon metabolism and the clinical consequences of disturbed folate metabolism are widely known. Folate status is a complex trait determined by both exogenous and endogenous factors. This study analyzed the association between 12 genetic variants and folate status in a Czech population with no folate fortification program. These 12 genetic variants were selected from 56 variant alleles found by resequencing the coding sequences and adjacent intronic regions of 6 candidate genes involved in folate metabolism or transport (FOLR1, FOLR2, FOLR3, MTHFR, PCFT, and RFC) from 29 individuals with low plasma and erythrocyte folate concentrations. Regression analyses of a cohort of 511 Czech controls not taking folate supplements revealed that only 2 variants in the MTHFR gene were associated with altered folate concentrations in plasma and/or erythrocytes. In our previous study, we observed that the common variant MTHFR c.665C > T (known as c.677C > T; p.A222V) was associated with decreased plasma folate concentrations. In the present study, we show in addition that the rare variant MTHFR c.1958C > T (p.T653M) is associated with significantly increased erythrocyte folate concentrations (P = 0.02). Multivariate regression analysis revealed that this uncommon variant, which is present in 2% of Czech control chromosomes, explains 0.9% of the total variability of erythrocyte folate concentrations; the magnitude of this effect size was comparable with that of the common MTHFR c.665C > T variant. This result indicates that the rare genetic variants may determine folate status to a similar extent as the common allelic variant.

Cystathionine gamma-lyase: Clinical, metabolic, genetic, and structural studies.

We report studies of six individuals with marked elevations of cystathionine in plasma and/or urine. Studies of CTH, the gene that encodes cystathionine gamma-lyase, revealed the presence among these individuals of either homozygous or compound heterozygous forms of a novel large deletion, p.Gly57_Gln196del, two novel missense mutations, c.589C>T (p.Arg197Cys) and c.932C>T (p.Thr311Ile), and one previously reported alteration, c.200C>T (p.Thr67Ile). Another novel missense mutation, c.185G>T (p.Arg62His), was found in heterozygous form in three mildly hypercystathioninemic members of a Taiwanese family. In one severely hypercystathioninemic individual no CTH mutation was found. Brief clinical histories of the cystathioninemic/cystathioninuric patients are presented. Most of the novel mutations were expressed and the CTH activities of the mutant proteins determined. The crystal structure of the human enzyme, hCTH, and the evidence available as to the effects of the mutations in question, as well as those of the previously reported p.Gln240Glu, on protein structure, enzymatic activity, and responsiveness to vitamin B(6) administration are discussed. Among healthy Czech controls, 9.3% were homozygous for CTH c.1208G>T (p.Ser403Ile), previously found homozygously in 7.5% of Canadians for whom plasma total homocysteine (tHcy) had been measured. Compared to wild-type homozygotes, among the 55 Czech c.1208G>T (p.Ser403Ile) homozygotes a greater level of plasma cystathionine was found only after methionine loading. Three of the four individuals homozygous or compound heterozygous for inactivating CTH mutations had mild plasma tHcy elevations, perhaps indicating a cause-and-effect relationship. The experience with the present patients provides no evidence that severe loss of CTH activity is accompanied by adverse clinical effects.

Birth prevalence of homocystinuria in Central Europe: frequency and pathogenicity of mutation c.1105C>T (p.R369C) in the cystathionine beta-synthase gene.

OBJECTIVES: To estimate the frequency of the cystathionine beta-synthase deficiency caused by c.1105C>T mutation in Central Europe compared to Norway, and to examine the pathogenicity of the corresponding p.R369C mutant enzyme. STUDY DESIGN: Mutation c.1105C>T was analyzed in 600 anonymous Czech newborn blood spots. Catalytic activity and quaternary structure of the p.R369C mutant was evaluated after expression in 2 cellular systems. RESULTS: Population frequency of the c.1105C>T mutation was 0.005, predicting the birth prevalence of homocystinuria of 1:40000, which increased to 1:15500 in a model including 10 additional mutations. In Escherichia coli the p.R369C mutant misfolded, and its activity was severely reduced, and expression in Chinese hamster ovary cells enabled proper folding with activity decreased to 63% of the wild-type enzyme. This decreased activity was not due to impaired K(m) for both substrates but resulted from V(max) lowered to 55% of the normal cystathionine beta-synthase enzyme. CONCLUSIONS: The c.1105C>T (p.R369C) allele is common also in the Czech population. Although the p.R369C mutation impairs folding and decreases velocity of the enzymatic reaction, our data are congruent with rather mild clinical phenotype in homozygotes or compound heterozygotes carrying this mutation.

Single-nucleotide polymorphisms in genes relating to homocysteine metabolism: how applicable are public SNP databases to a typical European population?

To facilitate the association studies in complex diseases characterized by hyperhomocysteinemia, we collected structural and frequency data on single-nucleotide polymorphism (SNPs) in 24 genes relating to homocysteine metabolism. Firstly, we scanned approximately 1.2 Mbp of sequence in the NCBI SNP database (dbSNP) build 110 and we detected 1353 putative SNPs with an average in silico genic density of 1:683. Out of 112 putative SNPs in coding regions (cSNPs), we selected a subset of 42 cSNPs and we assessed the applicability of the NCBI dbSNP to the Czech population - a typical representative of European Caucasians - by determining the frequency of the putative cSNPs experimentally by PCR-RFLP or ARMS-PCR in at least 110 control Czech chromosomes. As only 25 of the 42 analyzed cSNPs met the criterion of >/=1% frequency, the positive predictive value of the NCBI data set for our population reached 60%, which is similar to other studies. The correlation of SNP frequency between Czechs and other Caucasians - obtained from NCBI and/or literature - was stronger (r(2)=0.90 for 20 cSNPs) than between Czechs and general NCBI database entries (r(2)=0.73 for 27 cSNPs). Moreover, frequencies of all 20 putative cSNPs, for which data in Caucasians were available, were congruently below or above the 1% frequency criterion both in Czechs and in other Caucasians. In summary, our study shows that the NCBI dbSNP is a useful tool for selecting cSNPs for genetic studies of hyperhomocysteinemia in European populations, although experimental validation of SNPs should be performed, especially if the cSNP entry lacks any frequency data in Caucasians.

Genetic variants of homocysteine metabolizing enzymes and the risk of coronary artery disease.

It is unresolved whether elevated homocysteine in coronary artery disease (CAD) is the cause of arteriosclerosis or its consequence. In contrast, genetic variants of enzymes that metabolize homocysteine cannot be altered by arteriosclerosis. Consequently, their association with CAD would permit to imply causality. We modeled by regression analysis the effect of 11 variants in the methionine cycle upon CAD manifestation in 591 controls and 278 CAD patients. Among the examined variants only the carriership for the c.844ins68 in the cystathionine beta-synthase (CBS) gene was associated with a significantly lowered risk of CAD (OR=0.56; 95% CI=0.35-0.90 in the univariable, and OR=0.41, 95% CI=0.19-0.89 for obese people in the multivariable analysis, respectively). Healthy carriers of the c.844ins68 variant exhibited, compared to the wild type controls, significantly higher postload ratios of blood S-adenosylmethionine to S-adenosylhomocysteine (61.4 vs. 54.9, p=0.001) and of plasma total cysteine to homocysteine (8.6 vs. 7.3, p=0.004). The changes in these metabolites are compatible with an improved methylation status and with enhanced activity of homocysteine transsulfuration. In conclusion, the coincidence of clinical and biochemical effects of a common c.844ins68 CBS variant supports the hypothesis that compounds relating to homocysteine metabolism may play role in the development and/or progression of CAD.