Cysteamine revisited: repair of arginine to cysteine mutations.

Cysteamine is a small aminothiol endogenously derived from coenzyme A degradation. For some decades, synthetic cysteamine has been employed for the treatment of cystinosis, and new uses of the drug continue to emerge. In this review, we discuss the role of cysteamine in cellular and extracellular homeostasis and focus on the potential use of aminothiols to reconstitute the function of proteins harboring arginine (Arg) to cysteine (Cys) mutations, via repair of the Cys residue into a moiety that introduces an amino group, as seen in basic amino acid residues Lys and Arg. Cysteamine has been utilized in vitro and ex vivo in four different genetic disorders, and thus provides "proof of principle" that aminothiols can modify Cys residues. Other aminothiols such as mercaptoethylguanidine (MEG) with closer structural resemblance to the guanidinium moiety of Arg are under examination for their predicted enhanced capacity to reconstitute loss of function. Although the use of aminothiols holds clinical potential, more studies are required to refine specificity and treatment design. The efficacy of aminothiols to target proteins may vary substantially depending on their specific extracellular and intracellular locations. Redox potential, pH, and specific aminothiol abundance in each physiological compartment are expected to influence the reactivity and turnover of cysteamine and analogous drugs. Upcoming research will require the use of suitable cell and animal models featuring Arg to Cys mutations. Since, in general, Arg to Cys changes comprise about 8% of missense mutations, repair of this specific mutation may provide promising avenues for many genetic diseases.

Atopic dermatitis is not associated with actinic keratosis: cross-sectional results from the Rotterdam study.

BACKGROUND: Epidermal barrier impairment and an altered immune system in atopic dermatitis (AD) may predispose to ultraviolet-induced DNA damage. OBJECTIVES: To study the association between AD and actinic keratosis (AK) in a population-based cross-sectional study. METHODS: AD was defined by modified criteria of the U.K. working party's diagnostic criteria. AKs were diagnosed by physicians during a full-body skin examination, and keratinocyte cancers were identified via linkage to the national pathology database. The results were analysed in adjusted multivariable and multinomial models. RESULTS: A lower proportion of subjects with AD had AKs than those without AD: 16% vs. 24%, P = 0·002; unadjusted odds ratio (OR) 0·60, 95% confidence interval (CI) 0·42-0·83; adjusted OR 0·74, 95% CI 0·51-1·05; fully adjusted OR 0·69, 95% CI 0·47-1·07. In a multinomial model patients with AD were less likely to have ≥ 10 AKs (adjusted OR 0·28, 95% CI 0·09-0·90). No effect of AD on basal cell carcinoma or squamous cell carcinoma was found: adjusted OR 0·71, 95% CI 0·41-1·24 and adjusted OR 1·54, 95% CI 0·66-3·62, respectively. CONCLUSIONS: AD in community-dwelling patients is not associated with AK.

Arterial stiffness is not associated with bone parameters in an elderly hyperhomocysteinemic population.

Several studies have observed positive associations between bone disease and cardiovascular disease. A potential common pathway is hyperhomocysteinemia; however, to date, there is a lack of data regarding hyperhomocysteinemic populations. Therefore, we examined both cross-sectionally and longitudinally, whether there is an association between bone parameters and arterial stiffness in a hyperhomocysteinemic population, and investigated the potential common role of homocysteine (hcy) level on these associations. Cross-sectional and longitudinal data of the B-PROOF study were used (n = 519). At both baseline and 2-year follow-up we determined bone measures-incident fractures and history of fractures, bone-mineral density (BMD) and quantitative ultrasound (QUS) measurement. We also measured arterial stiffness parameters at baseline-pulse wave velocity, augmentation index and aortic pulse pressure levels with applanation tonometry. Linear regression analysis was used to examine these associations and we tested for potential interaction of hcy level. The mean age of the study population was 72.3 years and 44.3 % were female. Both cross-sectionally and longitudinally there was no association between arterial stiffness measures and BMD or QUS measurements or with incident fractures (n = 16) within the 2-3 years of follow-up. Hcy level did not modify the associations and adjustment for hcy did not change the results. Arterial stiffness was not associated with bone parameters and fractures, and hcy neither acted as a pleiotropic factor nor as a mediator. The potential association between bone and arterial stiffness is therefore not likely to be driven by hyperhomocysteinemia.

MRI and (1)H-MRS in adenosine kinase deficiency.

INTRODUCTION: Adenosine kinase deficiency (ADK deficiency) is a recently described disorder of methionine and adenosine metabolism resulting in a neurological phenotype with developmental delay, muscular hypotonia, and epilepsy as well as variable systemic manifestations. The underlying neuropathology is poorly understood. We have investigated MRI and (1)H-MRS changes in ADK deficiency in order to better understand the in vivo neuropathologic changes of ADK deficiency. METHODS: Systematic evaluation of 21 MRIs from eight patients (age range 9 days-14.6 years, mean 3.9 years, median 2.7 years) including diffusion-weighted imaging in six and (1)H-MRS in five patients. RESULTS: Brain maturation was delayed in the neonatal period and in infancy (6/6), but ultimately complete. White matter changes occurring in five of eight patients were discrete, periventricular, and unspecific (4/5), or diffuse with sparing of optic radiation, corona radiata, and pyramidal tracts (1/5). Choline was low in white matter spectra (3/3), while there was no indication of low creatine in white matter or basal ganglia (5/5), and diffusion was variably decreased or increased. Central tegmental tract hyperintensity was a common finding (6/8), as was supratentorial atrophy (6/8). CONCLUSIONS: MRI changes in ADK deficiency consist of delayed but ultimately completed brain maturation with later onset of mostly unspecific white matter changes and potentially transient central tegmental tract hyperintensity. Immaturity on neonatal MRI is consistent with prenatal onset of disease and reduced choline with lower membrane turnover resulting in delayed myelination and deficient myelin maintenance.

[Administration of intravenous sedation with midazolam by dentists is unsafe]. / Toediening van intraveneuze sedatie met midazolam door tandarts is onveilig.

In the December issue of the Nederlands Tijdschrift voor Tandheelkunde (Dutch Journal of Dentistry) in 2014, an article was devoted to the use of light sedation with midazolam by dentists. A number of dentists who are active in the area of Special Dentistry (anxiety management, care of the disabled) and a anesthesiologist offer a response to the article and argue that the administration of intravenous sedation with midazolam by dentists is unsafe.

STED microscopy: increased resolution for medical research?

Optical imaging is crucial for addressing fundamental problems in all areas of life science. With the use of confocal and two-photon fluorescence microscopy, complex dynamic structures and functions in a plethora of tissue and cell types have been visualized. However, the resolution of 'classical' optical imaging methods is poor due to the diffraction limit and does not allow resolution of the cellular microcosmos. On the other hand, the novel stimulated emission depletion (STED) microscopy technique, because of its targeted on/off-switching of fluorescence, is not hampered by a diffraction-limited resolution barrier. STED microscopy can therefore provide much sharper images, permitting nanoscale visualization by sequential imaging of individual-labelled biomolecules, which should allow previous findings to be reinvestigated and provide novel information. The aim of this review is to highlight promising developments in and applications of STED microscopy and their impact on unresolved issues in biomedical science.

B-vitamin levels and genetics of hyperhomocysteinemia are not associated with arterial stiffness.

BACKGROUND AND AIMS: Hyperhomocysteinemia is associated with arterial stiffness, but underlying pathophysiological mechanisms explaining this association are to be revealed. This study was aimed to explore two potential pathways concerning the one-carbon metabolism. A potential causal effect of homocysteine was explored using a genetic risk score reflecting an individual's risk of having a long-term elevated plasma homocysteine level and also associations with B-vitamin levels were investigated. METHODS AND RESULTS: Baseline cross-sectional data of the B-PROOF study were used. In the cardiovascular subgroup (n = 567, 56% male, age 72.6 ± 5.6 yrs) pulse wave velocity (PWV) was determined using applanation tonometry. Plasma concentrations of vitamin B12, folate, methylmalonic acid (MMA) and holo transcobalamin (holoTC) were assessed and the genetic risk score was based on 13 SNPs being associated with elevated plasma homocysteine. Associations were examined using multivariable linear regression analysis. B-vitamin levels were not associated with PWV. The genetic risk score was also not associated with PWV. However, the homocysteine-gene interaction was significant (p < 0.001) in the association of the genetic risk score and PWV. Participants with the lowest genetic risk of having long-term elevated homocysteine levels, but with higher measured homocysteine levels, had the highest PWV levels. CONCLUSION: Homocysteine is unlikely to be causally related to arterial stiffness, because there was no association with genetic variants causing hyperhomocysteinemia, whereas non-genetically determined hyperhomocysteinemia was associated with arterial stiffness. Moreover, the association between homocysteine and arterial stiffness was not mediated by B-vitamins. Possibly, high plasma homocysteine levels reflect an unidentified factor, that causes increased arterial stiffness.

A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase.

Hyperhomocysteinaemia has been identified as a risk factor for cerebrovascular, peripheral vascular and coronary heart disease. Elevated levels of plasma homocysteine can result from genetic or nutrient-related disturbances in the trans-sulphuration or re-methylation pathways for homocysteine metabolism. 5, 10-Methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5, 10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the predominant circulatory form of folate and carbon donor for the re-methylation of homocysteine to methionine. Reduced MTHFR activity with a thermolabile enzyme has been reported in patients with coronary and peripheral artery disease. We have identified a common mutation in MTHFR which alters a highly-conserved amino acid; the substitution occurs at a frequency of approximately 38% of unselected chromosomes. The mutation in the heterozygous or homozygous state correlates with reduced enzyme activity and increased thermolability in lymphocyte extracts; in vitro expression of a mutagenized cDNA containing the mutation confirms its effect on thermolability of MTHFR. Finally, individuals homozygous for the mutation have significantly elevated plasma homocysteine levels. This mutation in MTHFR may represent an important genetic risk factor in vascular disease.

Cellular hypomethylation is associated with impaired nitric oxide production by cultured human endothelial cells.

Hyperhomocysteinemia (HHcy) is a risk factor for vascular disease, but the underlying mechanisms remain incompletely defined. Reduced bioavailability of nitric oxide (NO) is a principal manifestation of underlying endothelial dysfunction, which is an initial event in vascular disease. Inhibition of cellular methylation reactions by S-adenosylhomocysteine (AdoHcy), which accumulates during HHcy, has been suggested to contribute to vascular dysfunction. However, thus far, the effect of intracellular AdoHcy accumulation on NO bioavailability has not yet been fully substantiated by experimental evidence. The present study was carried out to evaluate whether disturbances in cellular methylation status affect NO production by cultured human endothelial cells. Here, we show that a hypomethylating environment, induced by the accumulation of AdoHcy, impairs NO production. Consistent with this finding, we observed decreased eNOS expression and activity, but, by contrast, enhanced NOS3 transcription. Taken together, our data support the existence of regulatory post-transcriptional mechanisms modulated by cellular methylation potential leading to impaired NO production by cultured human endothelial cells. As such, our conclusions may have implications for the HHcy-mediated reductions in NO bioavailability and endothelial dysfunction.

The DizzyQuest: relation between self-reported hearing loss, tinnitus and objective hearing thresholds in patients with Meniere's disease.

BACKGROUND: Combining a mobile application-based vestibular diary called the DizzyQuest and an iPad-based hearing test enables evaluation of the relationship between experienced neuro-otological symptoms and hearing thresholds in daily life setting. The aim was to investigate the relationship between self-reported hearing symptoms and hearing thresholds in patients with Meniere's disease (MD), using the DizzyQuest and the iPad-based hearing test simultaneously. METHODS: The DizzyQuest was administered for 3 weeks in 21 patients. Using the experience-sampling-method (ESM), it assessed hearing loss and tinnitus severity for both ears separately. Each day after the DizzyQuest, an iPad-based hearing test was used to measure hearing thresholds. A mixed model regression analysis was performed to investigate relationships between hearing thresholds and self-reported hearing loss and tinnitus severity. RESULTS: Fifteen patients were included. Overall, pure-tone averages (PTAs) were not correlated with self-reported hearing loss severity and tinnitus. Individual differences in PTA results between both ears did not significantly influence the difference in self-reported hearing loss severity between both ears. Self-reported hearing loss and tinnitus scores were significantly higher in ears that corresponded with audiometric criteria of MD (p < 0.001). Self-reported tinnitus severity significantly increased with self-reported hearing loss severity in affected (p = 0.011) and unaffected ears (p < 0.001). CONCLUSION: Combining the DizzyQuest and iPad-based hearing test, facilitated assessment of self-reported hearing loss and tinnitus severity and their relationship with hearing thresholds, in a daily life setting. This study illustrated the importance of investigating neuro-otological symptoms at an individual level, using multiple measurements. ESM strategies like the DizzyQuest should therefore be considered in neuro-otological research.

Elevated concentrations of sedoheptulose in bloodspots of patients with cystinosis caused by the 57-kb deletion: implications for diagnostics and neonatal screening.

Cystinosis is an autosomal recessive lysosomal storage disease caused by mutations in CTNS. The most prevalent CTNS mutation is a homozygous 57-kb deletion that also includes an adjacent gene named SHPK (CARKL), encoding sedoheptulokinase. Patients with this deletion have elevated urinary concentrations of sedoheptulose. Using derivatisation with pentafluorobenzyl hydroxylamine and liquid chromatography-tandem mass spectrometry (LC-MS/MS), we developed a new sensitive method for the quantification of sedoheptulose in dried blood spots. This method can be utilized as a quick screening test to detect cystinosis patients homozygous for the 57-kb deletion in CTNS; which is the most common mutation of cystinosis. Sedoheptulose concentrations in the deleted patients were 6 to 23 times above the upper limit for controls. The assessment of sedoheptulose in a bloodspot from a known cystinosis patient homozygous for the 57-kb deletion retrieved from the Dutch neonatal screening program showed that sedoheptulose was already elevated in the neonatal period. There was no overlap in sedoheptulose levels between cystinosis patients homozygous for the 57-kb deletion and cystinosis patients not homozygous for this deletion. Our presented method can be used prior to mutation analysis to detect cystinosis patients homozygous for the 57-kb deletion. We feel that the presented method enables fast (pre)-symptomatic detection of cystinosis patients homozygous for the 57-kb deletion, allowing early treatment.

Value of Endolymphatic Hydrops and Perilymph Signal Intensity in Suspected Ménière Disease.

BACKGROUND AND PURPOSE: Ménière disease is characterized by endolymphatic hydrops, whereas perilymphatic enhancement on MR imaging has been suggested to be of additional value in diagnosing Ménière disease. This study evaluates the presence of endolymphatic hydrops and perilymphatic enhancement in patients with Ménière disease and with other vertigo-associated inner ear pathology. MATERIALS AND METHODS: A 3D-FLAIR sequence 4 hours after intravenous gadolinium injection was performed to visualize the endolymph and perilymph in 220 patients suspected of having Ménière disease. Patients' ears were retrospectively categorized as having Ménière disease (probable or definite) or other vertigo-associated inner ear pathology not attributable to Ménière disease. Endolymphatic hydrops was evaluated using a visual classification system, and perilymphatic enhancement was scored both visually and quantitatively. RESULTS: Endolymphatic hydrops was present in 137 (91.9%) of the definite Ménière disease ears and in 9 (7.0%) of the ears with other vertigo-associated inner ear pathology (P < .001). The combination of endolymphatic hydrops and visually increased perilymphatic enhancement was present in 122 (81.9%) definite Ménière disease ears compared with 4 (3.1%) ears with other vertigo-associated inner ear pathology (P < .001). This combination increases the positive predictive value from 0.94 for endolymphatic hydrops and 0.91 for perilymphatic enhancement to 0.97. The addition of measured perilymphatic enhancement leads to a moderate decrease in sensitivity from 0.92 for endolymphatic hydrops to 0.86. CONCLUSIONS: The combination of perilymphatic enhancement and endolymphatic hydrops in patients suspected of having Ménière disease increases the positive predictive value in the diagnosis of definite Ménière disease.

The DizzyQuest: to have or not to have a vertigo attack?

BACKGROUND: The DizzyQuest, an app-based vestibular diary, provides the opportunity to capture the number and nature of vertigo attacks in daily life. To accomplish this, the DizzyQuest provides different strategies: event sampling using an attack questionnaire, and time sampling using an evening questionnaire. Objective of this study was to investigate whether the number and nature of reported vertigo attacks was comparable between the two questionnaires. METHODS: Fifty-seven patients, who reported vertigo attacks, used the DizzyQuest for on average 24 days. The number and nature (including symptoms, triggers and duration) of vertigo attacks were compared between the attack and the evening questionnaire. RESULTS: The attack questionnaire was used 192 times. In contrast, at least 749 new vertigo attacks were reported in 446 evening questionnaires. A vertigo attack was not always reported in both questionnaires during the same day. Vertigo attacks that were most likely captured by both questionnaires were not always reported the same in both questionnaires regarding triggers and duration. CONCLUSION: Event sampling using an attack questionnaire has low recall bias and, therefore, reliably captures the nature of the attack, but induces a risk of under-sampling. Time sampling using an evening questionnaire suffers from recall bias, but seems more likely to capture less discrete vertigo attacks and it facilitates registration of the absence of vertigo attacks. Depending on the clinical or research question, the right strategy should be applied and participants should be clearly instructed about the definition of a vertigo attack.

Introducing the DizzyQuest: an app-based diary for vestibular disorders.

BACKGROUND: Most questionnaires currently used for assessing symptomatology of vestibular disorders are retrospective, inducing recall bias and lowering ecological validity. An app-based diary, administered multiple times in daily life, could increase the accuracy and ecological validity of symptom measurement. The objective of this study was to introduce a new experience sampling method (ESM) based vestibular diary app (DizzyQuest), evaluate response rates, and to provide examples of DizzyQuest outcome measures which can be used in future research. METHODS: Sixty-three patients diagnosed with a vestibular disorder were included. The DizzyQuest consisted of four questionnaires. The morning- and evening-questionnaires were administered once each day, the within-day-questionnaire 10 times a day using a semi-random time schedule, and the attack questionnaire could be completed after the occurrence of a vertigo or dizziness attack. Data were collected for 4 weeks. Response rates and loss-to-follow-up were determined. Reported symptoms in the within-day-questionnaire were compared within and between patients and subgroups of patients with different vestibular disorders. RESULTS: Fifty-one patients completed the study period. Average response rates were significantly higher than the desired response rate of > 50% (p < 0.001). The attack-questionnaire was used 159 times. A variety of neuro-otological symptoms and different disease profiles were demonstrated between patients and subgroups of patients with different vestibular disorders. CONCLUSION: The DizzyQuest is able to capture vestibular symptoms within their psychosocial context in daily life, with little recall bias and high ecological validity. The DizzyQuest reached the desired response rates and showed different disease profiles between subgroups of patients with different vestibular disorders. This is the first time ESM was used to assess daily symptoms and quality of life in vestibular disorders, showing that it might be a useful tool in this population.

Serum homocysteine levels in relation to clinical progression in multiple sclerosis.

BACKGROUND: Elevated homocysteine levels are associated with various neurodegenerative diseases and have even been identified as a risk factor for some of these. Homocysteine levels may be elevated in patients with multiple sclerosis (MS) but large studies are lacking and the relation with disease progression remains to be determined. AIM: The aim of the study was to investigate homocysteine levels in patients with MS and in controls, and to study the relationship between homocysteine levels and clinical progression in MS. METHODS: Serum homocysteine levels were compared between MS subtypes (n = 219) and controls (n = 152). Homocysteine levels were associated with baseline and follow-up clinical severity scores. RESULTS: The results showed that serum homocysteine values were similar in patients with MS and controls. Baseline scores on the Expanded Disability Status Scale were higher in patients with secondary progressive MS (SPMS) in the top compared with the bottom quartile of homocysteine levels (p = 0.02). The baseline scores on the Multiple Sclerosis Functional Composite (MSFC) and Paced Auditory Serial Addition Test (PASAT), which measures cognitive functioning, were lower in patients with SPMS in the top compared with the bottom quartile of homocysteine levels (MSFC, p = 0.02; PASAT, p = 0.02). High homocysteine levels were associated with a decline in PASAT scores during follow-up in patients with primary progressive MS (p = 0.009). CONCLUSION: Serum total homocysteine levels are associated with several measures of disease progression in MS but are not elevated in patients with MS compared with controls. The association of homocysteine levels with cognition in patients with progressive MS raises the question of whether homocysteine directly impacts on MS or reflects a more general neurodegenerative process.

Changes in markers of cobalamin status after cessation of oral B-vitamin supplements in elderly people with mild cobalamin deficiency.

Mildly cobalamin-deficient elderly were supplemented with 1000 microg cobalamin (group C, n=34), 1000 microg cobalamin with 400 microg folic acid (group CF, n=31) or a placebo (n=30) for 6 months. Participants provided one single blood sample 3, 5 or 7 months after cessation of supplementation to monitor early changes in plasma concentrations of cobalamin, holotranscobalamin (holoTC) and methylmalonic acid (MMA). At the end of supplementation (groups C+CF), one participant met our criteria for mild cobalamin deficiency, as did 13, 14 and 43% of the participants assessed at respectively 3, 5 and 7 months post-supplementation. Cobalamin and holoTC declined on average with 47 and 56% relative to concentrations at the end of supplementation for the group assessed at 7 months post-supplementation. Essentially similar declines were observed for those participants assessed at 3 and 5 months post-supplementation. Mean MMA concentrations increased by 15% (P=0.07) in those participants assessed at 3 and 5 months post-supplementation, and increased by 50% (P=0.002) in those participants assessed at 7 months post-supplementation. Considering MMA as a sensitive tissue marker for cobalamin status, oral supplementation may afford adequate cobalamin status for a period of up to 5 months after cessation in the majority of participants.

Transsulfuration in an adult with hepatic methionine adenosyltransferase deficiency.

We investigated sulfur and methyl group metabolism in a 31-yr-old man with partial hepatic methionine adenosyltransferase (MAT) deficiency. The patient's cultured fibroblasts and erythrocytes had normal MAT activity. Hepatic S-adenosylmethionine (SAM) was slightly decreased. This clinically normal individual lives with a 20-30-fold elevation of plasma methionine (0.72 mM). He excretes in his urine methionine and L-methionine-d-sulfoxide (2.7 mmol/d), a mixed disulfide of methanethiol and a thiol bound to an unidentified group X, which we abbreviate CH3S-SX (2.1 mmol/d), and smaller quantities of 4-methylthio-2-oxobutyrate and 3-methylthiopropionate. His breath contains 17-fold normal concentrations of dimethylsulfide. He converts only 6-7 mmol/d of methionine sulfur to inorganic sulfate. This abnormally low rate is due not to a decreased flux through the primarily defective enzyme, MAT, since SAM is produced at an essentially normal rate of 18 mmol/d, but rather to a rate of homocysteine methylation which is abnormally high in the face of the very elevated methionine concentrations demonstrated in this patient. These findings support the view that SAM (which is marginally low in this patient) is an important regulator that helps to determine the partitioning of homocysteine between degradation via cystathionine and conservation by reformation of methionine. In addition, these studies demonstrate that the methionine transamination pathway operates in the presence of an elevated body load of that amino acid in human beings, but is not sufficient to maintain methionine levels in a normal range.

Defective cystathionine beta-synthase regulation by S-adenosylmethionine in a partially pyridoxine responsive homocystinuria patient.

We determined the molecular basis of cystathionine beta-synthase (CBS) deficiency in a partially pyridoxine-responsive homocystinuria patient. Direct sequencing of the entire CBS cDNA revealed the presence of a homozygous G1330A transition. This mutation causes an amino acid change from aspartic acid to asparagine (D444N) in the regulatory domain of the protein and abolishes a TaqI restriction site at DNA level. Despite the homozygous mutation, CBS activities in extracts of cultured fibroblasts of this patient were not in the homozygous but in the heterozygous range. Furthermore, we observed no stimulation of CBS activity by S-adenosylmethionine, contrary to a threefold stimulation in control fibroblast extract. The mutation was introduced in an E. coli expression system and CBS activities were measured after addition of different S-adenosylmethionine concentrations (0-200 microM). Again, we observed a defective stimulation of CBS activity by S-adenosylmethionine in the mutated construct, whereas the normal construct showed a threefold stimulation in activity. These data suggest that this D444N mutation interferes in S-adenosylmethionine regulation of CBS. Furthermore, it indicates the importance of S-adenosylmethionine regulation of the transsulfuration pathway in homocysteine homeostasis in humans.

The MTHFR 677C->T polymorphism and the risk of congenital heart defects: a literature review and meta-analysis.

BACKGROUND: Periconceptional folic acid supplementation may protect against congenital heart defects (CHDs). Identification of candidate genes in folate metabolism has suggested that the 677C-->T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene may be particularly associated with the risk of CHDs. AIM: To assess the relationship between MTHFR 677C-->T and CHDs by literature review and meta-analysis. METHODS: Studies were identified by searches of electronic literature for papers focussing on MTHFR 677C-->T and the risk of any type of CHD. Both case-control comparisons and transmission-disequilibrium tests (TDTs) in family-based designs were included. RESULTS: We found 13 eligible studies. Of 10 case-control studies, four focused on the fetal polymorphism, two studied the maternal polymorphism, and a further four investigated both. Three further publications used a family-based association study to assess the effect of the T allele on cardiac development. Overall analysis yielded odds ratios of 1.3 (95%CI 0.97-1.73) and 1.2 (95%CI 0.83-1.74) for fetal and maternal MTHFR TT genotypes, respectively. TDTs revealed no association between fetal 677T allele and CHDs. DISCUSSION: This relatively small meta-analysis found no substantial evidence of increased CHD risk in individuals with MTHFR 677CT and TT genotypes. Heterogeneity regarding population background, study design and type of heart defects complicates the pooling and comparison of the studies. The effect of modification by periconceptional folic acid intake should be taken into account. Further larger studies and well-defined phenotypic subcategory analyses are needed to decide whether the MTHFR 677C-->T polymorphism of the affected child and/or their mother is truly a risk factor for the development of CHDs.

A genome-wide linkage scan for homocysteine levels suggests three regions of interest.

BACKGROUND: An elevated plasma total homocysteine (tHcy) level is a risk factor for many clinical conditions, including vascular disease and venous thrombosis. The tHcy levels are partly determined by genetic factors. Extensive candidate gene studies have identified several genetic variants, including the MTHFR 677C>T, that influence tHcy levels, but so far only part of the genetic variation in tHcy can be explained. OBJECTIVE: In order to identify chromosomal regions that influence tHcy levels, a genome-wide linkage analysis was conducted. PATIENTS/METHODS: Our study population consisted of 13 pedigrees and 469 subjects with data on fasting plasma tHcy levels. A set of 377 markers covering the genome was genotyped in 275 subjects. The variance component linkage method (SOLAR version 2.1.3) was used for the two-point and multipoint linkage analyses. RESULTS: The heritability of the age- and sex-adjusted homocysteine levels was 44%. The multipoint linkage analysis identified one region with suggestive linkage on chromosome 16q (LOD score 1.76; nominal P = 0.0024). Weaker evidence of linkage was found for regions on chromosome 12q (LOD score 1.57; nominal P = 0.0036) and chromosome 13q (LOD score 1.52; nominal P = 0.0041). CONCLUSIONS: In our families the plasma tHcy level was highly heritable. The multipoint linkage analysis identified three regions that showed weak to suggestive linkage to tHcy levels.