Decreased Methylenetetrahydrofolate Reductase Activity Research Articles

Study of A1298C MTHFR Gene Polymorphism as a Risk Factor for Neural Tube Defects in the Eastern Algerian Population

Background: As C677T mutation, A1298C mutation in methylene tetrahydrofolate reductase (MTHFR) gene results in a decreased MTHFR activity but to a less extent, it is known as a risk factor of predisposition to human neural tube defects (NTDs), in some populations. Our objective was therefore to study, for the first time in Algerian population, if A1298C polymorphism confers risk for the occurrence of this abnormality. We have examined the distribution of the genotype and the allele frequencies of A1298C mutation, and also their influence on plasma homocysteine (Hcy) concentration. Patients and Methods: We studied this polymorphism in 38 mothers of NTD cases and 67 control individuals of an eastern Algerian population. The mutation was determined by polymerase chain reaction-restriction fragment length polymorphism analysis (PCR/RFLP). Plasma homocysteine concentration was analyzed using an automated chemiluminescence method. Results: No signi?cant association could be observed between allele and genotypes frequencies of A1298C MTHFR gene polymorphism and NTDs risk. However, we could observe that A1298C polymorphism affects homocysteine metabolism in mothers of NTD cases leading to homocysteine concentration values higher in AA genotype and lower in AC/CC genotypes (15.29 ± 11.8 μmol/l vs. 8.63 ± 3.83 μmol/l, p Conclusion: Data indicate that A1298C MTHFR gene polymorphism might be a risk factor by affecting homocysteine metabolism in mothers of Algerian children with NTDs.

Riboflavin supplementation alters global and gene-specific DNA methylation in adults with the MTHFR 677 TT genotype

DNA methylation is important in regulating gene expression and genomic stability while aberrant DNA methylation is associated with disease. Riboflavin (FAD) is a cofactor for methylenetetrahydrofolate reductase (MTHFR), a critical enzyme in folate recycling, which generates methyl groups for homocysteine remethylation to methionine, the pre-cursor to the universal methyl donor S-adenosylmethionine (SAM). A polymorphism (C677T) in MTHFR results in decreased MTHFR activity and increased homocysteine concentration. Previous studies demonstrated that riboflavin modulates this phenotype in homozygous adults (MTHFR 677 TT genotype), however, DNA methylation was not considered. This study examined DNA methylation, globally and at key MTHFR regulatory sites, in adults stratified by MTHFR genotype and the effect of riboflavin supplementation on DNA methylation in individuals with the 677 TT genotype. Samples were accessed from participants, screened for the MTHFR C677T polymorphism, who participated in observational (n = 80) and targeted riboflavin (1.6 mg/day) RCTs (n = 80). DNA methylation at LINE-1 and key regulatory regions of the MTHFR locus were analysed by pyrosequencing in peripheral blood leukocytes. LINE-1 (+1.6%; p = 0.011) and MTHFR south shelf (+4.7%, p < 0.001) were significantly hypermethylated in individuals with the MTHFR 677 TT compared to CC genotype. Riboflavin supplementation resulted in decreased global methylation, albeit only significant at one CpG. A significant reduction in DNA methylation at the MTHFR north shore (−1.2%, p < 0.001) was also observed in TT adults following intervention with riboflavin. This provides the first RCT evidence that DNA methylation may be modulated by riboflavin in adults with the MTHFR 677 TT genotype.

Customized MethylC-Capture Sequencing to Evaluate Variation in the Human Sperm DNA Methylome Representative of Altered Folate Metabolism.

Background:The sperm DNA methylation landscape is unique and critical for offspring health. If gamete-derived DNA methylation escapes reprograming in early embryos, epigenetic defects in sperm may be transmitted to the next generation. Current techniques to assess sperm DNA methylation show bias toward CpG-dense regions and do not target areas of dynamic methylation, those predicted to be environmentally sensitive and tunable regulatory elements.Objectives:Our goal was to assess variation in human sperm DNA methylation and design a targeted capture panel to interrogate the human sperm methylome.Methods:To characterize variation in sperm DNA methylation, we performed whole genome bisulfite sequencing (WGBS) on an equimolar pool of sperm DNA from a wide cross section of 30 men varying in age, fertility status, methylenetetrahydrofolate reductase (MTHFR) genotype, and exposures. With our targeted capture panel, in individual samples, we examined the effect of MTHFR genotype ( 677CC, 677TT), as well as high-dose folic acid supplementation (, per genotype, before and after supplementation).Results:Through WGBS we discovered nearly 1 million CpGs possessing intermediate methylation levels (20–80%), termed dynamic sperm CpGs. These dynamic CpGs, along with 2 million commonly assessed CpGs, were used to customize a capture panel for targeted interrogation of the human sperm methylome and test its ability to detect effects of altered folate metabolism. As compared with MTHFR 677CC men, those with the 677TT genotype (50% decreased MTHFR activity) had both hyper- and hypomethylation in their sperm. High-dose folic acid supplement treatment exacerbated hypomethylation in MTHFR 677TT men compared with 677CC. In both cases, of altered methylation was found in dynamic sperm CpGs, uniquely measured by our assay.Discussion:Our sperm panel allowed the discovery of differential methylation following conditions affecting folate metabolism in novel dynamic sperm CpGs. Improved ability to examine variation in sperm DNA methylation can facilitate comprehensive studies of environment–epigenome interactions. https://doi.org/10.1289/EHP4812

Associations of Polymorphisms in MTHFR Gene with the Risk of Age-Related Cataract in Chinese Han Population: A Genotype-Phenotype Analysis.

Homocysteine (Hcy) is a potential risk factor for age-related cataract (ARC). Methylenetetrahydrofolate reductase (MTHFR) is the key enzyme for Hcy metabolism, and variants of MTHFR may affect MTHFR enzyme activity. This study mainly evaluated the associations between variants in MTHFR gene, plasma MTHFR enzyme activity, total Hcy (tHcy) levels and ARC risk in Chinese population. Four single nucleotide polymorphisms (SNPs) in MTHFR gene were genotyped using the high-resolution melting (HRM) method in 502 ARC patients (mean age, 70.2 [SD, 9.0], 46.0% male) and 890 healthy controls (mean age, 67.1 [SD, 11.1], 47.6% male). The plasma MTHFR activity, folic acid (FA), vitamins B12 and B6 levels were detected by enzyme-linked immunosorbent assays (ELISA). The plasma tHcy levels were measured by an automated enzymatic assay. After the Bonferroni correction, the minor allele T of SNP rs1801133 showed a significant association with an increased risk of overall ARC (OR = 1.26, P = 0.003). Consistent association was also found between SNP rs1801133 and cortical ARC risk (OR = 1.44, P = 0.003). Haplotype analyses revealed an adverse effect of the haplotype "C-A-T-C" (alleles in order of SNPs rs3737967, rs1801131, rs1801133 and rs9651118) on ARC risk (OR = 1.55, P = 0.003). Moreover, in a joint analysis of SNPs rs9651118 and rs1801133, subjects with two unfavorable genotypes had a 1.76-fold increased risk of ARC compared with the reference group, and a statistically significant dose-response trend (Ptrend = 0.001) was also observed. Further, in healthy controls and patients with cortical ARC, the allele T of SNP rs1801133 and the increasing number of unfavorable genotypes were significantly correlated with decreased MTHFR activity as well as increased tHcy levels. However, there was no significant association between FA, vitamins B12, B6 levels and MTHFR variants. Our data indicated that variants in MTHFR gene might individually and jointly influence susceptibility to ARC by affecting MTHFR enzyme activity and tHcy levels.

Methylene tetrahydrofolate reductase (MTHFR) gene polymorphisms in chronic myeloid leukemia: an Egyptian study

Methylenetetrahydrofolate reductase (MTHFR) gene plays a pivotal role in folate metabolism. Several genetic variations in MTHFR gene as MTHFR-C677T and MTHFR-A1298C result in decreased MTHFR activity, which could influence efficient DNA methylation and explain susceptibility to different cancers. The etiology of chronic myeloid leukemia (CML) is obscure and little is known about individual's susceptibility to CML. In order to assess the influence of these genetic polymorphisms on the susceptibility to CML and its effect on the course of the disease among Egyptians, we performed an age-gender-ethnic matched case-control study. The study included 97 CML patients and 130 healthy controls. Genotyping of MTHFR-C677T and -A1298C was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. The results showed no statistical difference in the distribution of MTHFR-C677T and -A1298C polymorphic genotypes between CML patients and controls. The frequency of MTHFR 677-TT homozygous variant was significantly higher in patients with accelerated/blastic transformation phase when compared to those in the chronic phase of the disease. In conclusion, our study revealed that MTHFR-C677T and -A1298C polymorphisms could not be considered as genetic risk factors for CML in Egyptians. However, MTHFR 677-TT homozygous variant might be considered as a molecular predictor for disease progression.

Methylenetetrahydrofolate reductase and methionine synthase reductase gene polymorphisms in ethnic Han women from Linyi

To explore the distribution of genetic polymorphisms of methylenetetrahydrofolate reductase (MTHFR) 677C/T, 1298A/C and methionine synthase reductase (MTRR) 66A/G among ethnic Han females from Linyi, and to correlate it with serum level of homocysteine (Hcy). A cross-sectional study was carried out. Oral epithelial cell samples were collected from 825 subjects. MTHFR and MTRR gene polymorphisms were determined with a Taqman-Minor Groove Binder (MGB) method. Distribution of gene polymorphisms was analyzed and compared with others regions of China including Weifang, Zhengzhou, Deyang and Hainan. A biochemical assay was also carried out to determine the total Hcy in plasma of 281 subjects. The reductase activity of MTHFR was classified into decreased and stable groups according to genetic polymorphism of MTHFR. Correlation between MTHFR groups and total Hcy level were also explored. (1) The frequencies of MTHFR677CC, CT and TT genotypes of the selected subjects were 16.7%, 48.3% and 35.0%, respectively. The frequencies of MTHFR 1298AA, AC and CC genotypes were 76.0%, 21.6% and 2.4%, respectively. And those of MTRR 66AA, AG and GG genotypes were 54.7%, 39.4% and 5.9%, respectively. For the selected subjects, their frequency of MTHFR 677TT genotype was higher than that of Deyang and Hainan (P< 0.01), whilst the frequency of MTHFR 1298CC genotype was lower than that of Deyang and Hainan (P < 0.01), and the frequency of MTRR 66 GG genotype was lower than that of Hainan (P< 0.01). (2) The Hcy level for those with decreased MTHFR activity was significantly higher than those with stable MTHFR activity (P< 0.05). MTHFR gene 677C/T, 1298A/C and MTRR 66A/G polymorphisms in ethnic Han women from Linyi have differed significantly from other regions of China. Decreased MTHFR activity caused by genetic polymorphisms is a risk factor for raised Hcy level.

Methotrexate-induced mucositis in acute leukemia patients is not associated with the MTHFR 677T allele in Mexico

Methylenetetrahydrofolate reductase (MTHFR) has two common variants with reduced activity due to polymorphisms at nucleotides 677 and 1298. Both affect folate metabolism and thus remethylation of homocysteine, but are also thought to affect nucleotide synthesis and DNA methylation. Methotrexate (MTX), which interrupts folate metabolism, is used in the treatment of a variety of diseases including acute lymphoblastic leukemia (ALL), but exerts in some patients toxic effects on fast dividing tissues such as mucosal epithelia. The enhanced toxicity may be due to cooperative effects between MTX and MTHFR variants. Accordingly, it has been reported that carrying the 677T allele of the MTHFR is a risk factor for MTX-associated mucositis. As in the Mexican population, which is characterized by a high prevalence of the 677T MTHFR variant, several of its commonly associated defects have not been observed, we investigated the relationship between MTX toxicity and the 677T allele. Out of 28 patients with ALL (CC: 2, CT: 10, TT: 16), 16 had episodes of MTX-associated mucositis (CC: 0, CT: 6, TT: 10). Neither at the gene level nor at the genotype level was a significant association with mucositis found. It may be postulated that the risk of higher MTX toxicity in patients with decreased MTHFR activity could be neutralized by the normally folate rich diet in Mexico.

Effect of the methylenetetrahydrofolate reductase C677T polymorphism on chemosensitivity of colon and breast cancer cells to 5-fluorouracil and methotrexate.

Although single nucleotide polymorphisms may be potentially important pharmacogenetic determinants of cancer therapy, functional evidence regarding their relevance is currently lacking. The C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene is associated with changes in cellular composition of folates. We hypothesized that this polymorphism may modulate the cytotoxic effect of 5-fluorouracil (5FU) and methotrexate (MTX), two commonly used chemotherapeutic agents for colon and breast cancers, because the modes of action of 5FU and MTX are critically dependent on cellular composition of folates. Human HCT116 colon and MDA-MB-435 breast cancer cells were stably transfected with wild-type or mutant 677T human MTHFR cDNA. MTHFR enzyme activity and thermolability, intracellular folate composition, growth rate, and catalytic thymidylate synthase activity were determined. In vitro chemosensitivity to 5FU and MTX was determined using the sulforhodamine B assay. In vivo chemosensitivity of HCT116 cells to 5FU was determined in nude mice. Compared with cells expressing the wild-type MTHFR, HCT116 and MDA-MB-435 cells expressing the mutant 677T MTHFR had decreased MTHFR activity, MTHFR thermolability, changed intracellular folate distribution, accelerated cellular growth rate, and increased thymidylate synthase activity. The MTHFR 677T mutation increased chemosensitivity of colon and breast cancers to 5FU, but decreased chemosensitivity of breast cancer cells to MTX. In nude mice, xenografts expressing the mutant 677T MTHFR grew faster, but were more sensitive to 5FU, than xenografts expressing the wild-type protein. Our data provide evidence that the MTHFR C677T polymorphism affects the concentration and intracellular distribution of folates and changes the growth and chemosensitivity of colon and breast cancer cells. The MTHFR C677T polymorphism may be a useful pharmacogenetic determinant for providing rational and effective tailored chemotherapy.

The Methylenetetrahydrofolate Reductase 677 C→T Polymorphism and Preeclampsia in Two Populations

In Brief OBJECTIVE The C677T polymorphism of the 5,10 methylenetetrahydrofolate reductase (MTHFR) gene is associated with decreased MTHFR activity and elevated plasma homocysteine levels with the result of an increased risk for vascular disease. Because thrombosis of the maternal spiral arteries can be one of the causative events in the disease, it has been suggested that the C677T polymorphism may also play a role in the pathogenesis of preeclampsia. Our case-control study investigated the prevalence of the 677T allele in two ethnically different populations and the potential association of the 677T allele with preeclampsia. Special attention was paid to the potential contribution of the fetal genotype to disease risk. METHODS Blood samples were collected from 81 mothers and 61 newborns after preeclampsia and 99 mothers and 61 newborns with normal pregnancies. Genomic DNA was amplified by polymerase chain reaction with locus-specific primers, and presence of the polymorphism was determined by enzymatic digestion with HinfI and visualization on polyacrylamide gels. RESULTS Genotypes carrying the MTHFR 677T allele were significantly more frequent in German-Croatians than in Indonesians in both patients and controls (P = .0033 in controls). In contrast, the prevalence of genotypes with the 677T allele was not increased among patients with preeclampsia compared with controls in both ethnic groups (P > .5 in all groups). In Germans, the frequency of 677T homozygotes among controls even exceeded that observed in preeclamptic patients (677T/T genotype frequency 0.20 in controls and 0.07 in patients). We did not find an increased prevalence of paternally inherited 677T alleles in preeclamptic fetuses relative to controls or other signs of maternal-fetal transmission distortion. CONCLUSION In our study, the MTHFR C677T polymorphism was not associated with an increased risk for preeclampsia on the level of the maternal or fetal genotype. However, significant differences of the frequency of genotypes carrying the 677T allele between Middle-Europeans and Indonesians were identified. The frequency of the methylenetetrahydrofolate reductase C677T polymorphism in mothers and newborns is significantly different in Middle-Europeans and Indonesians, but is not associated with preeclampsia.

The methylenetetrahydrofolate reductase 677 C→T polymorphism and preeclampsia in two populations

OBJECTIVE: The C677T polymorphism of the 5,10 methylenetetrahydrofolate reductase (MTHFR) gene is associated with decreased MTHFR activity and elevated plasma homocysteine levels with the result of an increased risk for vascular disease. Because thrombosis of the maternal spiral arteries can be one of the causative events in the disease, it has been suggested that the C677T polymorphism may also play a role in the pathogenesis of preeclampsia. Our case-control study investigated the prevalence of the 677T allele in two ethnically different populations and the potential association of the 677T allele with preeclampsia. Special attention was paid to the potential contribution of the fetal genotype to disease risk. METHODS: Blood samples were collected from 81 mothers and 61 newborns after preeclampsia and 99 mothers and 61 newborns with normal pregnancies. Genomic DNA was amplified by polymerase chain reaction with locus-specific primers, and presence of the polymorphism was determined by enzymatic digestion with HinfI and visualization on polyacrylamide gels. RESULTS: Genotypes carrying the MTHFR 677T allele were significantly more frequent in German-Croatians than in Indonesians in both patients and controls ( P = .0033 in controls). In contrast, the prevalence of genotypes with the 677T allele was not increased among patients with preeclampsia compared with controls in both ethnic groups ( P > .5 in all groups). In Germans, the frequency of 677T homozygotes among controls even exceeded that observed in preeclamptic patients (677T/T genotype frequency 0.20 in controls and 0.07 in patients). We did not find an increased prevalence of paternally inherited 677T alleles in preeclamptic fetuses relative to controls or other signs of maternal-fetal transmission distortion. CONCLUSION: In our study, the MTHFR C677T polymorphism was not associated with an increased risk for preeclampsia on the level of the maternal or fetal genotype. However, significant differences of the frequency of genotypes carrying the 677T allele between Middle-Europeans and Indonesians were identified.

Prevalence of common mutations of the MTHFR gene in a Puerto Rican population

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme in the metabolism of folate to methionine Fourteen severe mutations of the MTHFR gene have been found to result in only a 0-20 percent activity of the control MTHFR protein (Goyette, 1995). A common mutation (C677T), which results in high homocysteine and low plasma folate levels, has been associated with a thermolabile form of the MTHFR enzyme, therefore being a risk factor for cardiovascular diseases and neural tube defects (NTD) in the homozygous form (Frosst, 1995). Another mutation in the human MTHFR gene (A1298C) has been found to destroy an MboII recognition site and results in decreased MTHFR activity. Plasma and homocysteine levels are not altered with the A1298C mutation, however this mutation seems to be a risk factor when combined with the C677T mutation (Van der Put NM, 1998).In a prevalence study of the common C677T mutation screening in healthy women and newborn samples was performed we found that 8.6% of the individuals where homozygous for the mutation. These results compare with those found for Ohio Caucasian and Dublin populations (McAndrew, Kirke; 1996). Thirty NTD affected and control families were also analyzed in our laboratory for the C677T and A1298C mutations. Analysis of the A1298C mutation in 51 and 62 individuals from the control and NTD affected families, respectively, resulted in 8 control and 0 NTD affected individuals homozygous for the mutation. Taken together, the results of this study indicates that the Puerto Rican population has a low frecuency of the C677T mutation and confirms that homozygocity for the A1298C mutation does not present a direct risk for NTD. Supported by an RCMI Clinical Research Infrastructure Initiative (RCRII) Award IP20RR11126, National Center for Research Resources, RCMI Human Molecular Genetics Unit, NCRR-NIH RCMI Grant G12RR03051, and the Hereditary Disease Program, Department of Pediatrics, UPR, School of Medicine.

Plasma homocysteine levels related to interactions between folate status and methylenetetrahydrofolate reductase: A study in 52 healthy subjects

Hyperhomocysteinemia, a risk factor for vascular disease, is related to vitamin B 12, vitamin B 6, and especially folate deficiency, or to genetic factors such as mutations in methylenetetrahydrofolate reductase (MTHFR), an enzyme involved in the remethylation pathway of homocysteine to methionine. Recently, a C677 → T mutation identified in the MTHFR gene was found to be frequently associated with decreased MTHFR activity and an elevated plasma homocysteine concentration. Since hyperhomocysteinemia seems to be determined by both genetic and environmental factors, we studied the interactions between MTHFR (phenotype and genotype) and folate status, including methyltetrahydrofolate (methylTHF), the product of MTHFR, on the homocysteine concentration in 52 healthy subjects, (28 women and 24 men; mean age, 32.7 years). MTHFR activity seems to be dependent on folate status, as shown by a lower activity in folate-deficient subjects and a return to normal values after supplementation with folic acid, and also by a decreased enzymatic activity on phytohemagglutinin (PHA)- stimulated lymphocytes grown in a folic acid-deficient medium. Conversely, the C677 → T mutation seems to influence folate metabolism. Subjects who were homozygous for this mutation (+/+) had significantly higher plasma homocysteine and lower plasma folate and total and methylfolate levels in red blood cells (RBCs) than heterozygous (+/−) and normal (−/−) subjects. The ratio of RBC methylfolate to RBC total folate was, respectively, 0.27 in +/+, 0.66 in +/−, and 0.71 in −/−. This mutation seems to have an impact on methylTHF generation. These data illustrate the interactions between nutritional and genetic factors.

A Second Common Mutation in the Methylenetetrahydrofolate Reductase Gene: An Additional Risk Factor for Neural-Tube Defects?

Recently, we showed that homozygosity for the common 677(C-->T) mutation in the methylenetetrahydrofolate reductase (MTHFR) gene, causing thermolability of the enzyme, is a risk factor for neural-tube defects (NTDs). We now report on another mutation in the same gene, the 1298(A-->C) mutation, which changes a glutamate into an alanine residue. This mutation destroys an MboII recognition site and has an allele frequency of .33. This 1298(A-->C) mutation results in decreased MTHFR activity (one-way analysis of variance [ANOVA] P < .0001), which is more pronounced in the homozygous than heterozygous state. Neither the homozygous nor the heterozygous state is associated with higher plasma homocysteine (Hcy) or a lower plasma folate concentration-phenomena that are evident with homozygosity for the 677(C-->T) mutation. However, there appears to be an interaction between these two common mutations. When compared with heterozygosity for either the 677(C-->T) or 1298(A-->C) mutations, the combined heterozygosity for the 1298(A-->C) and 677(C-->T) mutations was associated with reduced MTHFR specific activity (ANOVA P < .0001), higher Hcy, and decreased plasma folate levels (ANOVA P <.03). Thus, combined heterozygosity for both MTHFR mutations results in similar features as observed in homozygotes for the 677(C-->T) mutation. This combined heterozygosity was observed in 28% (n =86) of the NTD patients compared with 20% (n =403) among controls, resulting in an odds ratio of 2.04 (95% confidence interval: .9-4.7). These data suggest that the combined heterozygosity for the two MTHFR common mutations accounts for a proportion of folate-related NTDs, which is not explained by homozygosity for the 677(C-->T) mutation, and can be an additional genetic risk factor for NTDs.

Decreased methylene tetrahydrofolate reductase activity due to the 677C?T mutation in families with spina bifida offspring

Decreased methylene tetrahydrofolate reductase activity due to the 677C?T mutation in families with spina bifida offspring

Decreased methylene tetrahydrofolate reductase activity due to the 677C-->T mutation in families with spina bifida offspring.

Periconceptional folate intake reduces both the occurrence and recurrence risk of neural tube defects. Plasma homocysteine levels can be elevated in mothers of a child with a neural tube defect, suggesting a dysfunctional folate metabolism. Very recently we showed that a common 677C-->T mutation in the 5,10-methylene tetrahydrofolate reductase gene, causing thermolability of the enzyme, is a risk factor for spina bifida offspring. Restriction enzyme analysis of the genomic 5,10-methylene tetrahydrofolate reductase polymerase chain reaction fragment revealed a significantly higher prevalence of a +/+ genotype among spina bifida patients and their mothers. The risk for spina bifida offspring is the strongest if both the mother and her child have the mutation in the homozygous state. Enzymatic analysis showed that homozygosity for the 677C-->T mutation causes a decreased 5,10-methylene tetrahydrofolate reductase activity, resulting in elevated plasma homocysteine and red blood cell folate levels and lowered plasma folate and cysteine values. This extended study demonstrates that a nucleotide substitution in the coding region of 5,10-methylene tetrahydrofolate reductase, resulting in reduced activity and an impaired homocysteine and folate metabolism, is a genetic risk factor for spina bifida.

Mutated methylenetetrahydrofolate reductase as a risk factor for spina bifida

Periconceptional folate supplementation reduces the risk of neural-tube defects. We studied the frequency of the 677C→T mutation in the 5,10–methylenetetrahydrofolate reductase (MTHFR) gene in 55 patients with spina bifida and parents of such patients (70 mothers, 60 fathers), 5% of 207 controls were homozygous for the 677C→T mutation compared with 16% of mothers, 10% of fathers, and 13% of patients. The mutation was associated with decreased MTHFR activity, low plasma folate, and high plasma homocysteine and red-cell folate concentrations. The 677C→T mutation should be regarded as a genetic risk factor for spina bifida.

Homocystinuria associated with decreased methylenetetrahydrofolate reductase activity

A new type of homocystinuria is described. A variety of evidence indicates that patients with this type of homocystinuria are not deficient in cystathionine synthase activity. Fibroblasts from these patients were unable to grow as rapidly as control fibroblasts if homocystine replaced methionine in the culture medium. N5-Methyltetrahydrofolate-homocysteine methyltransferase activity in these cells was not markedly decreased, whereas methylenetetrahydrofolate reductase activity was significantly below normal. A deficiency of this reductase activity can explain the biochemical abnormalities in these patients.