Polymorphism C776G in the transcobalamin II gene and homocysteine, folate and vitamin B12 concentrations. Association with MTHFR C677T and A1298C and MTRR A66G polymorphisms in healthy children

Exploring the Interplay Between Vitamin B12-related Biomarkers, DNA Methylation, and Gene-Nutrition Interaction in Esophageal Precancerous Lesions

BACKGROUND

Vitamin B12 depletion has been suggested to be associated with esophageal precancerous lesions (EPL). However, the potential mechanisms remain unclear.

AIMS

This study aims to evaluate the role of vitamin B12 and its regulated epigenetic modification in EPL and provide preliminary information on the identification of potential molecular biomarkers for the early prediction of EPL.

METHODS

We collected information and samples from the Early Diagnosis and Early Treatment Project of Esophageal Cancer database from 200 EPL cases and 200 matched controls. Vitamin B12, one-carbon metabolism biomarkers, genetic polymorphism of TCN2 C776G, and DNA methylation were compared. Preliminarily identified candidate promoters of differentially methylated CpG positions were further verified by targeted bisulfite sequencing.

RESULTS

EPL cases had significantly lower serum levels of vitamin B12 and transcobalamin II, and higher serum levels of homocysteine and 5-methyltetrahydrofolate than controls. The TCN2 C776G polymorphism was found to be associated with susceptibility to EPL and may interact with vitamin B12 nutritional status to influence the risk of EPL in male subjects. In addition, global hypomethylation related to vitamin B12 depletion was observed in EPL cases, along with region-specific hypermethylation of UGT2B15 and FGFR2 promoters.

CONCLUSIONS

This study suggests that vitamin B12 depletion may be associated with aberrant DNA methylation and increased risk of EPL through the one-carbon metabolism pathway, presents that the TCN2 C776G polymorphism may interact with vitamin B12 nutritional status to affect EPL risk in males, and also identifies specific locations in the UGT2B15 and FGFR2 promoters with potential as promising molecular biomarkers.

Comparison of TCN-2 (776C>G) Gene Polymorphism and Vitamin B12 Status with Different Body Mass Index among Saudi Adults

BACKGROUND

Overweight and obesity (OO) are significant public health issues, and many elements, including genetics, epigenetics, sedentary lifestyle, comorbid conditions, psychological and environmental pressures, have been linked to OO. More than 2 billion people are presently impacted by the global obesity epidemic, which is still advancing relentlessly. It is a significant public health concern and a major contributor to healthcare costs, because it increases the chance of developing conditions such as heart disease, stroke, type 2 diabetes, and chronic kidney disease (CKD). Using the ranges of 18.5-25 for normality, 25-30 for overweight, and 30 for obesity, BMI (in kg/m²) is used to identify obesity. Vitamin deficiency is one of the causative factors associated with the increasing trend of obesity. Altered vitamin B12 status is a multifactorial trait; changes in B12 status are produced by several single nucleotide polymorphisms (SNPs) in various genes that interact with the environment. They also support coordinated efforts to alter the built environment that is causing the obesity pandemic. Therefore, the present study aimed to evaluate the TCN-2 (776C>G) gene alteration and vitamin B12 levels with respect to different body mass index, as well as associating BMI with other biochemical parameters.

METHODS

250 individuals were involved in the study; among them, 100 were in the healthy weight range category (BMI: 18.5 to <25 kg/m²), 100 were overweight (BMI: 25.0 to <30 kg/m²), and 50 were obese (BMI: >30 kg/m²). Participants visited during the screening program were subjected to blood pressure measurement, and further peripheral blood samples were drawn from all the participants in plain as well as in EDTA vials for biochemical (lipid profile and vitamin B12 level) analysis and single nucleotide polymorphism studies. Extracted DNA from whole blood collected in EDTA vials using kit protocol was used for genotyping by PCR-RFLP.

RESULTS

The levels of systolic (p < 0.0001) and diastolic blood pressures (p < 0.0001), HDL (p < 0.0001), LDL (p = 0.04), TG (p < 0.0001), cholesterol (p < 0.0001), and VLDL (p < 0.0001) showed significant differences between healthy controls, overweight, and obese groups. The healthy control TCN-2 (776C>G) genotypes were compared with those of overweight and obese participants, and compared to the healthy controls it was observed that overweight (p = 0.01) and obese (p = 0.002) subjects had significant differences in TCN-2 (776C>G) genotypes. For genotypes CG and GG, the odds ratio was 1.61 (0.87-2.95; p = 0.12), and 3.81 (1.47-9.88; p = 0.005) for overweight participants, respectively, and obese participants' calculated odds ratios were 2.49 (1.16-5.36; p = 0.01) and 5.79 (1.93-17.35; p = 0.001), respectively. The relative risk for genotypes CG and GG, was 1.25 (0.93-1.68; p = 0.12), 2.17 (1.12-4.17; p = 0.02) for overweight participants, while the obese participants' calculated relative risks were 1.31 (1.03-1.68; p = 0.01) and 2.02 (1.12-3.65; p = 0.001), respectively. Vitamin B12 levels were analyzed, and it was observed that a significant difference existed among overweight (305.5 pmol/L, p < 0.0001) and obese patients (229 pmol/L, p < 0.0001), respectively, as compared to healthy controls (385.5 pmol/L). Correlation analysis showed a significant association of vitamin B12 level with TG, cholesterol and VLDL; it showed a negative correlation, suggesting that decreases in B12 levels may impact the lipid profile.

CONCLUSION

The study concluded that a predisposition to the GG genotype of TCN-2 gene polymorphism (776C>G) may increase susceptibility to obesity and the related complications, and higher odds and relative risk for the GG genotype may increase the risk of having obesity and further related complications. Lower vitamin B12 levels were linked with obesity and overweight, and impaired lipid parameters suggested that lower vitamin B12 may impact the altered lipid profile.

Evaluation of Vitamin B12, Folate and Ferritin Serum Levels in Jordanian Population

Vitamin B12, folate, and ferritin are vital for the development of the nervous system, blood formation, and diverse metabolic functions. The aim of the current study is to evaluate the status of vitamin B12, folate and ferritin in the Jordanian population across distinct geographical locations. In this retrospective study, the cohort population included 2,880 Jordanian individuals with an average age of 47 y for males and 34 y for females (January 2014-December 2016). Vitamin B12, folate, and ferritin were measured in the blood samples by immunoassay on an automated instrument. Prevalence of low levels of vitamin B12 among males and females was similar across the four regions (24%). Equivalently high levels of folate were reported in males (24.4%) and females (23.4%). Additionally, 37.4% of males and 20.4% of females showed low levels of ferritin. Pearson's correlations did not show any association between age, vitamin B12, folate, and ferritin levels in both sexes. Univariate odd ratio (OR) and age-adjusted OR in males showed a significant decrease in low vitamin B12 risk in the region of Tafela when compared to Irbid. In conclusion, our results showed a significant difference in vitamin B12 levels between populations according to their geographical locations. Ferritin levels were low in almost a quarter of the Jordanian population with a high prevalence in males and females in Irbid and Maan, respectively. These differences might be associated with the genetic, dietary and lifestyle situation which requires further studies to elucidate the risk factors for vitamin B12 and ferritin deficiency.

Homologous G776G Variant of Transcobalamin-II Gene is Linked to Vitamin B12 Deficiency

Vitamin B12 (Cobalamin) deficiency, due to improper internalization of cobalamin, is a metabolic disorder prevalent in impoverished and elderly populations and is associated with megaloblastic anemia and dementia. It has been suggested that mutations in transcobalamin II (TCN2) or gastric intrinsic factor (GIF) proteins can alter their binding efficiency to cobalamin or reduce the ability of their receptors to internalize them. In this case-control study, the correlation between vitamin B12 deficiency and alternative alleles of TCN2 and GIF was investigated in a Jordanian population. One hundred individuals with vitamin B12 deficiency (B12 < 200 mg/mL) were enrolled in our study to evaluate the TCN2 and GIF polymorphisms. The control group (B12 > 200 mg/mL) included 100 individuals. Our results indicated a significant association between the homologous variant of the TCN2 gene (G776G) and vitamin B12 deficiency, and an intermediate phenotype in heterozygous individuals (p < 0.001, OR = 5.6, 95% CI = 2.95 to 10.63). The GIF gene, however, showed no correlation between the A68G variant and vitamin B12 deficiency (p = 0.2). This study expounds the association of TCN2 polymorphism with cobalamin levels in a Jordanian population and highlights the necessity of further studies to elucidate the molecular basis and impact of TCN2 and GIF genes polymorphisms on vitamin B12 deficiency and associated disorders.

An update on vitamin B12-related gene polymorphisms and B12 status

Background

Vitamin B12 is an essential micronutrient in humans needed for health maintenance. Deficiency of vitamin B12 has been linked to dietary, environmental and genetic factors. Evidence for the genetic basis of vitamin B12 status is poorly understood. However, advancements in genomic techniques have increased the knowledge-base of the genetics of vitamin B12 status. Based on the candidate gene and genome-wide association (GWA) studies, associations between genetic loci in several genes involved in vitamin B12 metabolism have been identified.

Objective

The objective of this literature review was to identify and discuss reports of associations between single-nucleotide polymorphisms (SNPs) in vitamin B12 pathway genes and their influence on the circulating levels of vitamin B12.

Methods

Relevant articles were obtained through a literature search on PubMed through to May 2017. An article was included if it examined an association of a SNP with serum or plasma vitamin B12 concentration. Beta coefficients and odds ratios were used to describe the strength of an association, and a P < 0.05 was considered as statistically significant. Two reviewers independently evaluated the eligibility for the inclusion criteria and extracted the data.

Results

From 23 studies which fulfilled the selection criteria, 16 studies identified SNPs that showed statistically significant associations with vitamin B12 concentrations. Fifty-nine vitamin B12-related gene polymorphisms associated with vitamin B12 status were identified in total, from the following populations: African American, Brazilian, Canadian, Chinese, Danish, English, European ancestry, Icelandic, Indian, Italian, Latino, Northern Irish, Portuguese and residents of the USA.

Conclusion

Overall, the data analyzed suggests that ethnic-specific associations are involved in the genetic determination of vitamin B12 concentrations. However, despite recent success in genetic studies, the majority of identified genes that could explain variation in vitamin B12 concentrations were from Caucasian populations. Further research utilizing larger sample sizes of non-Caucasian populations is necessary in order to better understand these ethnic-specific associations.

Meat Consumption During Pregnancy and Substance Misuse Among Adolescent Offspring: Stratification of TCN2 Genetic Variants

BACKGROUND

Reducing meat consumption is often advised; however, inadvertent nutritional deficiencies during pregnancy may result in residual neurodevelopmental harms to offspring. This study assessed possible effects of maternal diets in pregnancy on adverse substance use among adolescent offspring.

METHODS

Pregnant women and their 13-year-old offspring taking part in a prospective birth cohort study, the Avon Longitudinal Study of Parents and Children (ALSPAC), provided Food Frequency Questionnaire data from which dietary patterns were derived using principal components analysis. Multivariable logistic regression models including potential confounders evaluated adverse alcohol, cannabis, and tobacco use of the children at 15 years of age.

RESULTS

Lower maternal meat consumption was associated with greater problematic substance use among 15-year-old offspring in dose-response patterns. Comparing never to daily meat consumption after adjustment, risks were greater for all categories of problem substance use: alcohol, odds ratio OR = 1.75, 95% CI = (1.23, 2.56), p < 0.001; tobacco use OR = 1.85, 95% CI = (1.28, 2.63), p < 0.001; and cannabis OR = 2.70, 95% CI = (1.89, 4.00), p < 0.001. Given the likelihood of residual confounding, potential causality was evaluated using stratification for maternal allelic variants that impact biological activity of cobalamin (vitamin B12) and iron. Lower meat consumption disproportionally increased the risks of offspring substance misuse among mothers with optimally functional (homozygous) variants (rs1801198) of the gene transcobalamin 2 gene (TCN2) which encodes the vitamin B12 transport protein transcobalamin 2 implicating a causal role for cobalamin deficits. Functional maternal variants in iron metabolism were unrelated to the adverse substance use. Risks potentially attributable to cobalamin deficits during pregnancy include adverse adolescent alcohol, cannabis, and tobacco use (14, 37, and 23, respectively).

CONCLUSIONS

Lower prenatal meat consumption was associated with increased risks of adolescent substance misuse. Interactions between TCN2 variant status and meat intake implicate cobalamin deficiencies.

A missense mutation in TCN2 is associated with decreased risk for congenital heart defects and may increase cellular uptake of vitamin B12 via Megalin

Deregulation of folate and vitamin B12 (VB12) metabolism contributes to the risk of congenital heart defects (CHDs). Transcobalamin (TCN2) is essential for transporting VB12 from blood to cells as TCN2-bound VB12 (holo-TC) is the only form for somatic cellular uptake. In this study, we performed an association study between common polymorphisms in 46 one carbon metabolism genes and CHD in 412 CHDs and 213 controls. Only two significant association signals in coding regions were identified: FTCD c.1470C>T & TCN2 c.230A>T. The only missense mutation, TCN2 c.230A>T, was further validated in 412 CHDs and 1177 controls. TCN2 c.230T is significantly associated with reduced CHD risk in North Chinese (odds ratio = 0.67, P = 4.62e-05), compared with the 230A allele. Interestingly, the mean level of plasma holo-TC in women with the TA genotype was 1.77-fold higher than that in women with the AA genotype. Further analysis suggested that c.230A>T enhanced the cellular uptake of holo-TC via the LRP2 receptor. Our results determined that a functional polymorphism in TCN2 contributes to the prevalence of CHDs. TCN2 c.230A>T is significantly associated with a reduced CHD risk, likely due to TCN2 c.230T improving the interaction between holo-TC and its LRP2 receptor.

Presence of t(14;18) translocation in healthy individuals varies according to ethnic background in the Brazilian population

Several groups have demonstrated that healthy individuals can present the t(14;18) translocation. In this report, the presence of the translocation was examined in healthy blood donors in Brazil, a country considered an ethnic melting pot. The translocation was detected by nested PCR in 227 peripheral blood samples from individuals with different ethnic backgrounds. The t(14;18) translocation was found in 45 of 85 White individuals (52.94%); in 57 of 72 Black individuals (79.17%); and in 68 of 70 individuals (97.14%) of Japanese-descent. In conclusion, the frequency of the t(14;18) translocation in the Brazilian population varies according to the ethnic background.

B vitamin polymorphisms and behavior: evidence of associations with neurodevelopment, depression, schizophrenia, bipolar disorder and cognitive decline

The B vitamins folic acid, vitamin B12 and B6 are essential for neuronal function, and severe deficiencies have been linked to increased risk of neurodevelopmental disorders, psychiatric disease and dementia. Polymorphisms of genes involved in B vitamin absorption, metabolism and function, such as methylene tetrahydrofolate reductase (MTHFR), cystathionine β synthase (CβS), transcobalamin 2 receptor (TCN2) and methionine synthase reductase (MTRR), have also been linked to increased incidence of psychiatric and cognitive disorders. However, the effects of these polymorphisms are often quite small and many studies failed to show any meaningful or consistent associations. This review discusses previous findings from clinical studies and highlights gaps in knowledge. Future studies assessing B vitamin-associated polymorphisms must take into account not just traditional demographics, but subjects' overall diet, relevant biomarkers of nutritional status and also analyze related genetic factors that may exacerbate behavioral effects or nutritional status.

Detection of Plasmodium falciparum and Plasmodium vivax subclinical infection in non-endemic region: implications for blood transfusion and malaria epidemiology

Background

In Brazil, malaria is endemic in the Amazon River basin and non-endemic in the extra-Amazon region, which includes areas of São Paulo state. In this state, a number of autochthonous cases of malaria occur annually, and the prevalence of subclinical infection is unknown. Asymptomatic infections may remain undetected, maintaining transmission of the pathogen, including by blood transfusion. In these report it has been described subclinical Plasmodium infection in blood donors from a blood transfusion centre in São Paulo, Brazil.

Methods

In this cross-sectional study, representative samples of blood were obtained from 1,108 healthy blood donors at the Fundação Pró-Sangue Hemocentro de São Paulo, the main blood transfusion centre in São Paulo. Malaria exposure was defined by the home region (exposed: forest region; non-exposed: non-forest region). Real-time PCR was used to detect Plasmodium falciparum and Plasmodium vivax. Subclinical malaria cases were geo-referenced.

Results

Eighty-four (7.41%) blood donors tested positive for Plasmodium; 57 of these were infected by P. falciparum, 25 by P. vivax, and 2 by both. The prevalence of P. falciparum and P. vivax was 5.14 and 2.26, respectively. The overall prevalence ratio (PR) was 3.23 (95% confidence interval (CI) 2.03, 5.13); P. falciparum PR was 16.11 (95% CI 5.87, 44.21) and P. vivax PR was 0.47 (95% CI 0.2, 1.12). Plasmodium falciparum subclinical malaria infection in the Atlantic Forest domain was present in the mountain regions while P. vivax infection was observed in cities from forest-surrounded areas.

Conclusions

The presence of Plasmodium in healthy blood donors from a region known as non-endemic, which is important in the context of transfusion biosafety, was described. Infected recipients may become asymptomatic carriers and a reservoir for parasites, maintaining their transmission. Furthermore, P. falciparum PR was positively associated with the forest environment, and P. vivax was associated with forest fragmentation.

Genetic polymorphisms modulate the folate metabolism of Brazilian individuals with Down syndrome

Individuals with Down syndrome (DS) carry three copies of the Cystathionine β-synthase (CβS) gene. The increase in the dosage of this gene results in an altered profile of metabolites involved in the folate pathway, including reduced homocysteine (Hcy), methionine, S-adenosylhomocysteine (SAH) and S-adenosylmethionine (SAM). Furthermore, previous studies in individuals with DS have shown that genetic variants in genes involved in the folate pathway influence the concentrations of this metabolism's products. The purpose of this study is to investigate whether polymorphisms in genes involved in folate metabolism affect the plasma concentrations of Hcy and methylmalonic acid (MMA) along with the concentration of serum folate in individuals with DS. Twelve genetic polymorphisms were investigated in 90 individuals with DS (median age 1.29 years, range 0.07-30.35 years; 49 male and 41 female). Genotyping for the polymorphisms was performed either by polymerase chain reaction (PCR) based techniques or by direct sequencing. Plasma concentrations of Hcy and MMA were measured by liquid chromatography-tandem mass spectrometry as previously described, and serum folate was quantified using a competitive immunoassay. Our results indicate that the MTHFR C677T, MTR A2756G, TC2 C776G and BHMT G742A polymorphisms along with MMA concentration are predictors of Hcy concentration. They also show that age and Hcy concentration are predictors of MMA concentration. These findings could help to understand how genetic variation impacts folate metabolism and what metabolic consequences these variants have in individuals with trisomy 21.

Transcobalamin polymorphism 67A->G, but not 776C->G, affects serum holotranscobalamin in a cohort of healthy middle-aged men and women

Two polymorphic variants in the gene coding for transcobalamin II (TCN2), TCN2 776C- > G and TCN2 67A- > G, may alter serum holotranscobalamin (holoTC), which in turn may affect cellular uptake of cobalamin (Cbl) and thereby Cbl status indicators. We studied the effects of TCN2 776C- > G and TCN2 67A- > G on blood concentrations of holoTC, Cbl, methylmalonic acid (MMA), and total homocysteine (tHcy) in 2411 individuals (50-64 y) that had been selected on the basis of these TCN2 genotypes from 10601 Norwegian inhabitants. The serum holoTC concentration was lower in TCN2 67AG (55 ± 0.75 pmol/L) and 67GG (48 ± 2.14 pmol/L) than in 67AA (62 ± 0.67 pmol/L) (P < 0.001) but did not differ among TCN2 776C- > G genotypes. The polymorphisms interacted as serum holoTC determinants (P = 0.001) and the presence of TCN2 67AG and GG in strata of 776CC and CG, but not 776GG, increased the risk of having serum holoTC < 45.6 pmol/L [tertile 1 vs. tertiles 2 and 3: OR = 2.5 (95% CI 1.8-3.5) for 67AG; OR = 5.7 (95% CI 3.5-9.1) for 67GG in 776CC; OR = 2.1 (95% CI 1.6-2.9) for 67AG; and OR = 4.5 (95% CI 2.4-8.2) for 67GG in 776CG; all P < 0.001]. Plasma MMA, tHcy, and Cbl were not affected by either polymorphism. In summary, serum holoTC, but not plasma Cbl, MMA, or tHcy, varied according to TCN2 67A- > G genotypes. It remains to be determined whether this polymorphic effect on serum holoTC alters its diagnostic utility as Cbl status indicator.

Polymorphisms in folate-related enzyme genes in idiopathic infertile Brazilian men

The aim of the study was to analyze the distribution of the methylenetetrahydrofolate reductase (MTHFR), methionine synthase reductase (MTRR), and methionine synthase (MTR) polymorphisms in idiopathic infertile Brazilian men and fertile men. Case-control study comprising 133 idiopathic infertile Brazilian men with nonobstructive azoospermia ([NOA] n = 55) or severe oligozoospermia ([SO] n = 78) and 173 fertile men as controls. MTHFR C677T, A1298C, and G1793A; MTRR A66G; and MTR A2756G polymorphisms were studied by quantitative polymerase chain reaction (qPCR). The results were analyzed statistically and a P value <.05 was considered significant. Single-marker analysis revealed a significant association among MTHFR C677T polymorphism and both NOA group (P = .018) and SO group (P < .001). Considering the MTHFR A1298C, MTHFR G1793A, and MTRR A66G polymorphisms, no difference was found between NOA group and SO group. Regarding the MTR A2756G polymorphism, a significant difference was found between NOA and controls, P = .017. However, statistical analysis revealed no association between SO group and controls. Combined genotypes of 3 MTHFR polymorphisms did not identify a haplotype associated with idiopathic infertility. The combinatory analysis of the 3 polymorphisms MTHFR, MTRR, and MTR did not show difference between cases and controls. The findings suggest the MTHFR C677T and MTR A2756G polymorphisms could be an important genetic factor predisposing to idiopathic infertility in Brazilian men.

Transcobalamin C776G genotype modifies the association between vitamin B12 and homocysteine in older Hispanics

Background

A common polymorphism, C776G, in the plasma B12 transport protein transcobalamin (TC), encodes for either proline or arginine at codon 259. This polymorphism may affect the affinity of TC for B12 and subsequent delivery of B12 to tissues.

Methods

TC genotype and its associations with indicators of B12 status, including total B12, holotranscobalamin (holoTC), methylmalonic acid, and homocysteine, were evaluated in a cohort of elderly Latinos (N=554, age 60–93y) from the Sacramento Area Latino Study on Aging (SALSA).

Results

The distribution of TC genotypes was 41.3% homozygous reference (776CC) and 11.6% homozygous variant (776GG). No differences between the homozygous genotypes were observed in total B12, holoTC, methylmalonic acid, or homocysteine. The holoTC/total B12 ratio was lower in the 776GG group compared with the 776CC group (p=0.04). Significant interactions of TC genotype with total B12 (p=0.04) and with holoTC (p≤0.03) were observed such that mean homocysteine concentrations and the odds ratios for hyperhomocysteinemia (>13 µmol/L) were higher in the 776CC subjects compared with all carriers of the G allele (776CG and 776GG combined) when total B12 (<156 pmol/L) or holoTC (<35 pmol/L) were low.

Conclusions

This population of older Latinos has a lower prevalence of the TC 776GG variant than reported for Caucasian populations. The association between vitamin B12 and homocysteine concentrations is modified by TC 776 genotype. It remains to be determined if the TC C776G polymorphism has a significant effect on the hematological and neurological manifestations of B12 deficiency or on vascular and other morbidities associated with hyperhomocysteinemia.

Vitamin B-12 and homocysteine status among vegetarians: a global perspective

Evidence exists that well-planned vegetarian diets provide numerous health benefits and are appropriate for all stages of the life cycle. It is also known that animal foods provide micronutrients that are nonexistent or available only in limited amounts in plant foods. Restriction or exclusion of all animal foods may therefore result in low intake of certain micronutrients such as vitamin B-12, thereby affecting vitamin B-12 status and elevating plasma homocysteine concentrations. Overall, the studies we reviewed showed reduced mean vitamin B-12 status and elevated mean homocysteine concentrations in vegetarians, particularly among vegans. Low vitamin B-12 intake may lead to decreased bioavailability and functional deficiency of cobalamin. Although early noticeable symptoms of vitamin B-12 deficiency are nonspecific (unusual fatigue, digestion problems, frequent upper respiratory infections), the best-known clinical manifestations of cobalamin malabsorption are hematologic (pernicious anemia) and neurologic symptoms. Hyperhomocysteinemia is associated with an increased risk of atherosclerosis and cardiovascular disease. Given these health concerns, vegetarians, particularly vegans, must be advised to carefully plan their diets, to monitor their plasma vitamin B-12 on a regular basis to facilitate early detection of low cobalamin status, and to use vitamin B-12-fortified foods or take vitamin B-12 supplements if necessary.

Genetic variants of methionine metabolism and X-ALD phenotype generation: results of a new study sample

X-linked adrenoleukodystrophy (X-ALD) is the most common inherited leukodystrophy. Nevertheless, no genotype-phenotype correlation has been established so far. Unidentified modifier genes or other cofactors are suspected to modulate phenotype and prognosis. We recently described polymorphisms of methionine metabolism as possible disease modifiers in X-ALD. To retest these findings, we analyzed 172 new DNA samples of X-ALD patients from different populations (France, Germany, USA, China) by genotyping eight genetic variants of methionine metabolism, including DHFR c.594+59del19bp, CBS c.844_855ins68, MTR c.2756A>G, MTHFR c.677C>T and c.1298A>C, MTRR c.60A>G, RFC1 c.80G>A, and Tc2 c.776C>G. We compared three X-ALD phenotypes: childhood-onset cerebral demyelinating inflammatory type (CCALD; n = 82), adulthood onset with focal cerebral demyelination (ACALD; n = 38), and adulthood onset without cerebral demyelination (AMN; n = 52). The association of genotypes and phenotypes was analyzed with univariate two-sided Pearson's chi(2). In the comparison between AMN and CCALD, the G allele of Tc2 c.776C>G was associated with X-ALD phenotypes (chi(2) = 6.1; P = 0.048). The prevalence of the GG genotype of Tc2 c.776C>G was higher in patients with CNS demyelination compared to those without CNS demyelination (chi(2) = 4.42; P = 0.036). The GG genotype was also more frequent in CCALD compared to AMN (chi(2) = 4.7; P = 0.031). The other polymorphisms did not show any significant associations in this study sample. Whereas the influence of other polymorphisms of methionine metabolism was not confirmed, the present study supports the previously made observation that the Tc2 genotype contributes to X-ALD phenotype generation.