Insights into Severe 5,10-Methylenetetrahydrofolate Reductase Deficiency: Molecular Genetic and Enzymatic Characterization of 76 Patients

Evidence for interaction of 5,10-methylenetetrahydrofolate reductase (MTHFR) with methylenetetrahydrofolate dehydrogenase (MTHFD1) and general control nonderepressible 1 (GCN1)

5,10-Methylenetetrahydrofolate reductase (MTHFR) is a folate cycle enzyme required for the intracellular synthesis of methionine. MTHFR was previously shown to be partially phosphorylated at 16 residues, which was abrogated by conversion of threonine 34 to alanine (T34A) or truncation of the first 37 amino acids (i.e. expression of amino acids 38-656), and promoted by methionine supplementation. Here, we over-expressed wild-type MTHFR (MTFHRWT), as well as the variants MTHFRT34A and MTHFR38-656 in 293T cells to provide further insights into these mechanisms. We demonstrate that following incubation in high methionine conditions (100-1000 μM) MTHFRWT is almost completely phosphorylated, but in methionine restricted conditions (0-10 μM) phosphorylation is reduced, while MTHFRT34A always remains unphosphorylated. Following affinity purification coupled mass spectrometry of an empty vector, MTHFRWT, MTHFRT34A and MTHFR38-656 in three separate experiments, we identified 134 proteins consistently pulled-down by all three MTHFR protein variants, of which 5 were indicated to be likely true interactors (SAINT prediction threshold of 0.95 and 2 fold-change). Amongst these were the folate cycle enzyme methylenetetrahydrofolate dehydrogenase (MTHFD1) and the amino acid starvation sensor general control nonderepressible 1 (GCN1). Immunoprecipitation-immunoblotting of MTHFRWT replicated interaction with both proteins. An AlphaFold 3 generated model of the MTHFR-MTHFD1 interaction places the MTHFD1 dehydrogenase/cyclohydrolase domain in direct contact with the MTHFR catalytic domain, suggesting their interaction may facilitate direct delivery of methylenetetrahydrofolate. Overall, we confirm methionine availability increases MTHFR phosphorylation, and identified potential interaction of MTHFR with MTHFD1 and GCN1.

Arabidopsis METHYLENETETRAHYDROFOLATE REDUCTASE 2 functions independently of PENETRATION 2 during primary immunity against rice blast

Non-host resistance (NHR) is the most durable and robust form of innate immunity, with a surge of interest in its role in crop improvement. Of the NHR genes identified against rice blast, a devastating disease caused by Magnaporthe oryzae, Arabidopsis PEN2 is indispensable for pre-penetration resistance to M. oryzae, while a consortium of genes orchestrates post-penetration resistance via lesser known mechanisms. We identified M. oryzae-susceptible mosA (mthfr2 pen2-3) from a randomly mutagenized Arabidopsis pen2-3 population using forward genetics. Analysis of T-DNA-inserted mthfr2 lines and pen2-3-complemented mosA lines revealed that MTHFR2-dependent resistance to M. oryzae is independent of PEN2. MTHFR2-defective plants exhibited higher accumulation of reactive oxygen species and expression of salicylic acid-dependent defense markers. MTHFR2-ligand docking revealed that A55V non-synonymous substitution in mosA altered ligand binding efficiency. This further affected the metabolomic profile of mosA, effectively allowing in vitro germination and development of M. oryzae conidia. Moreover, the loss-of-function mutation in mthfr2 (involved in the 1C metabolic pathway) potentiated mosA immunity against Pst DC3000. In conclusion, our findings showed that MTHFR2 is a positive modulator of NHR against M. oryzae. This work documents another layer of conserved yet divergent metabolomic defense in Arabidopsis regulated by folate-mediated 1C metabolism that has the potential to revolutionize crop improvement.

RNA sequencing combined with whole-exome sequencing revealed familial homocystinemia due to MTHFR deficiency and its complex splicing events

5,10-Methylenetetrahydrofolate reductase (MTHFR, MIM #607093) is a key enzyme in the folate cycle that catalyzes the conversion of 5,10-methylenetetrahydrofolate (5,10-MTHF) to 5-methyltetrahydrofolate (5-methylTHF), a critical step for the remethylation of homocysteine to methionine. Methylenetetrahydrofolate reductase deficiency is an autosomal recessive disease and the most common congenital defect in folate metabolism. A deficiency in MTHFR results in elevated serum homocysteine levels. In this study, we evaluated a patient diagnosed with epilepsy and elevated homocysteine levels, who carried compound heterozygous variants c.781-6G>A and c.1316T>C in the MTHFR gene. We primarily focused on the unreported non-canonical splicing variants c.781-6G>A in this patient and identified several complex splicing variant patterns. The c.1316T>C variant results in a substitution of leucine at position 439 with proline and this variant has been previously reported and is considered pathogenic. Our study mainly utilized RNA-seq and TA cloning to reveal the complex splicing patterns exhibited by this non-canonical splicing variant. Additionally, this finding was confirmed through in vitro experiments. This provided deeper insights into the underlying reasons for the patient's disease manifestation. Furthermore, despite apparently normal circulating folate and vitamin B12, we found two family members to exhibit mildly elevated homocysteine levels. While these individuals did not present overt clinical symptoms, the potential harm associated with high homocysteine levels should not be overlooked. This study not only provides additional genetic evidence for the clinical diagnosis of the patient but also broadens our understanding of the clinical manifestations of MTHFR deficiency.

Preconceptional and Periconceptional Folic Acid Supplementation in the Visegrad Group Countries for the Prevention of Neural Tube Defects

Neural tube defects (NTDs) are malformations of the central nervous system that represent the second most common cause of congenital morbidity and mortality, following cardiovascular abnormalities. Maternal nutrition, particularly folic acid, a B vitamin, is crucial in the etiology of NTDs. FA plays a key role in DNA methylation, synthesis, and repair, acting as a cofactor in one-carbon transfer reactions essential for neural tube development. Randomized trials have shown that FA supplementation during preconceptional and periconceptional periods reduces the incidence of NTDs by nearly 80%. Consequently, it is recommended that all women of reproductive age take 400 µg of FA daily. Many countries have introduced FA fortification of staple foods to prevent NTDs, addressing the high rate of unplanned pregnancies. These policies have increased FA intake and decreased NTD incidence. Although the precise mechanisms by which FA protects against NTDs remain unclear, compelling evidence supports its efficacy in preventing most NTDs, leading to national recommendations for FA supplementation in women. This review focuses on preconceptional and periconceptional FA supplementation in the female population of the Visegrad Group countries (Slovakia, Czech Republic, Poland, and Hungary). Our findings emphasize the need for a comprehensive approach to NTDs, including FA supplementation programs, tailored counseling, and effective national-level policies.

Novel methylenetetrahydrofolate reductase (MTHFR) mutation presenting with neonatal encephalopathy, hair loss and marfanoid features

We present a case of a male term neonate with lethargy, hypotonia, hypoventilation and severe encephalopathy. The infant had a history of two siblings who died in the neonatal period from unclear causes. The infant exhibited skin and hair abnormalities, including desquamation of the extremities, angular stomatitis, cheilitis, neonatal acne and thin, sparse hair. Additionally, the infant had a tall stature; long, slender fingers and toes; and facial dysmorphism characterised by a long, narrow face with increased interpalpebral distance. The condition deteriorated rapidly, and unfortunately, death occurred before a definitive diagnosis could be established. Tandem mass spectrometry suggested low methionine and clinical exome sequencing identified a nonsense mutation in the MTHFR gene.

Dynamic inter-domain transformations mediate the allosteric regulation of human 5, 10-methylenetetrahydrofolate reductase

5,10-methylenetetrahydrofolate reductase (MTHFR) commits folate-derived one-carbon units to generate the methyl-donor S-adenosyl-L-methionine (SAM). Eukaryotic MTHFR appends to the well-conserved catalytic domain (CD) a unique regulatory domain (RD) that confers feedback inhibition by SAM. Here we determine the cryo-electron microscopy structures of human MTHFR bound to SAM and its demethylated product S-adenosyl-L-homocysteine (SAH). In the active state, with the RD bound to a single SAH, the CD is flexible and exposes its active site for catalysis. However, in the inhibited state the RD pocket is remodelled, exposing a second SAM-binding site that was previously occluded. Dual-SAM bound MTHFR demonstrates a substantially rearranged inter-domain linker that reorients the CD, inserts a loop into the active site, positions Tyr404 to bind the cofactor FAD, and blocks substrate access. Our data therefore explain the long-distance regulatory mechanism of MTHFR inhibition, underpinned by the transition between dual-SAM and single-SAH binding in response to cellular methylation status.

Molecular Mechanisms Provide a Landscape for Biomarker Selection for Schizophrenia and Schizoaffective Psychosis

Research evaluating the role of the 5,10-methylenetetrahydrofolate reductase (MTHFR C677T) gene in schizophrenia has not yet provided an extended understanding of the proximal pathways contributing to the 5-10-methylenetetrahydrofolate reductase (MTHFR) enzyme's activity and the distal pathways being affected by its activity. This review investigates these pathways, describing mechanisms relevant to riboflavin availability, trace mineral interactions, and the 5-methyltetrahydrofolate (5-MTHF) product of the MTHFR enzyme. These factors remotely influence vitamin cofactor activation, histamine metabolism, catecholamine metabolism, serotonin metabolism, the oxidative stress response, DNA methylation, and nicotinamide synthesis. These biochemical components form a broad interactive landscape from which candidate markers can be drawn for research inquiry into schizophrenia and other forms of mental illness. Candidate markers drawn from this functional biochemical background have been found to have biomarker status with greater than 90% specificity and sensitivity for achieving diagnostic certainty in schizophrenia and schizoaffective psychosis. This has implications for achieving targeted treatments for serious mental illness.

Identification of a Potential Antimycobacterial Drug Sensitizer Targeting a Flavin-Independent Methylenetetrahydrofolate Reductase

The increasing antibiotic resistance of Mycobacterium tuberculosis and pathogenic nontuberculosis mycobacteria highlights the urgent need for new prevention and treatment strategies. Recently, the cocrystal structure of a Mycobacterium smegmatis flavin-independent 5,10-methylenetetrahydrofolate reductase (MsmMTHFR) that binds with a reduced nicotinamide adenine dinucleotide (NADH) has been well-determined, providing a structural basis for the screening of antimycobacterial leads targeting MsmMTHFR, a new enzyme involved in tetrahydrofolic acid (THF) biosynthesis. In this study, we identified compound AB131 as a promising candidate that fits well into the NADH binding pocket of MsmMTHFR through virtual screening. We discovered that AB131 and its derivatives (13 and 14) can sensitize the antimycobacterial activity of the antitubercular drug para-aminosalicyclic acid (PAS) by 2-5-fold against various species of mycobacteria. Although the compounds themselves do not exhibit any antimycobacterial activity, the high binding affinity of AB131 with MsmMTHFR or Rv2172c was evaluated by microscale thermophoresis analysis. Additionally, we predicted and validated the key residues (V115, V117, P118, and R163) of MsmMTHFR that are involved in the interaction with AB131 by using molecular docking and mutagenesis analysis. These findings offer a potential exploitable target for developing potent and specific antimycobacterial drug sensitizers.

Evaluation of the clinical, biochemical, and genetic presentation of neonatal and adult-onset 5,10-methylene tetrahydrofolate reductase (MTHFR) deficiency in patients from Pakistan

OBJECTIVES

To study the biochemical, clinical and molecular characteristics of 5,10- methylenetetrahydrofolate reductase (MTHFR) deficiency in Pakistani patients from a single center.

METHODS

Medical charts, urine organic acid chromatograms, plasma methionine and Hcys levels, and molecular testing results of MTHFR gene of patients presenting at the Biochemical Genetics Clinic, AKUH from 2016 to 2022 were reviewed.

RESULTS

Neonatal MTHFR deficiency was found in five patients. The median (IQR) age of symptom onset and diagnosis were 18 (8.5-22) and 26 (16.5-31) days. The median lag between symptom onset and diagnosis was 8 (4.5-12.5) days. The median age of treatment initiation and duration of treatment were 26 (16.5-49) and 32 (25.5-54) days. The most common clinical features were lethargy, poor feeding, and seizures. The MTHFR gene sequencing revealed homozygous variants p.K510K, p.R567*, and p.R157W. Renal insufficiency manifesting as elevated serum creatinine and responding to betaine therapy was noted in one patient. This has not been previously reported in neonatal MTHFR deficiency and may reflect engagement of alternate pathways of remethylation. Adult onset MTHFR deficiency was found in six patients, with a heterogeneous neurological presentation. The median lag between symptoms onset and diagnosis was 7 (3-11) years. MTHFR gene sequencing revealed homozygous variant p.A195V in five patients from one family and p.G261V in the other. Two of the five reported variants are novel that include p.R157W and p.G261V.

CONCLUSIONS

Eleven patients of this rare disorder from a single center indicate the need for clinical awareness and appropriate biochemical evaluation to ensure optimal outcomes.

Contribution of Genetic Test to Early Diagnosis of Methylenetetrahydrofolate Reductase (MTHFR) Deficiency: The Experience of a Reference Center in Southern Italy

BACKGROUND

the deficiency of 5,10-Methylenetetrahydrofolate reductase (MTHFR) constitutes a rare and severe metabolic disease and is included in most expanded newborn screening (NBS) programs worldwide. Patients with severe MTHFR deficiency develop neurological disorders and premature vascular disease. Timely diagnosis through NBS allows early treatment, resulting in improved outcomes.

METHODS

we report the diagnostic yield of genetic testing for MTHFR deficiency diagnosis, in a reference Centre of Southern Italy between 2017 and 2022. MTHFR deficiency was suspected in four newborns showing hypomethioninemia and hyperhomocysteinemia; otherwise, one patient born in pre-screening era showed clinical symptoms and laboratory signs that prompted to perform genetic testing for MTHFR deficiency.

RESULTS

molecular analysis of the MTHFR gene revealed a genotype compatible with MTHFR deficiency in two NBS-positive newborns and in the symptomatic patient. This allowed for promptly beginning the adequate metabolic therapy.

CONCLUSIONS

our results strongly support the need for genetic testing to quickly support the definitive diagnosis of MTHFR deficiency and start therapy. Furthermore, our study extends knowledge of the molecular epidemiology of MTHFR deficiency by identifying a novel mutation in the MTHFR gene.

In silico drug screen reveals potential competitive MTHFR inhibitors for clinical repurposing

MTHFR (Methylenetetrahydrofolate reductase) is a pivotal enzyme involved in one-carbon metabolism, which is critical for the proliferation of cancer cells. In line with this, published literature showed that MTHFR knockdown caused impaired growth of multiple types of cancer cells. Moreover, higher MTHFR expression levels were linked to shorter overall survival in hepatocellular carcinoma, adrenocortical carcinoma, and low-grade glioma, bringing the need to design MTHFR inhibitors as a possible treatment option. No competitive inhibitors of MTHFR have been reported as of today. This study aimed to identify potential competitive MTHFR inhibitor candidates using an in silico drug screen. A total of 30470 molecules containing biogenic compounds, FDA-approved drugs, and those in clinical trials were screened against the catalytic pocket of MTHFR in the presence and absence of cofactors. Binding energy and ADMET analysis revealed that Vilanterol (β2-adrenergic agonist), Selexipag (prostacyclin receptor agonist), and Ramipril Diketopiperazine (ACE inhibitor) are potential competitive inhibitors of MTHFR. Molecular dynamics analyses and MM-PBSA calculations with these compounds particularly revealed the amino acids between 285-290 for ligand binding and highlighted Vilanterol as the strongest candidate for MTHFR inhibition. Our results could guide the development of novel MTHFR inhibitor compounds, which could be inspired by the drugs brought into the spotlight here. More importantly, these potential candidates could be quhickly tested as a repurposing strategy in pre-clinical and clinical studies of the cancers mentioned above.Communicated by Ramaswamy H. Sarma.

Doubly bi-allelic variants of MTHFR and MTHFD1 in a Chinese patient with hyperhomocysteinemia and failure of folic acid therapy

Background: Hyperhomocysteinemia (HHcy) is a risk factor for thromboembolic disease. Defects in one-carbon metabolism (1-CM)-related genes, such as methylenetetrahydrofolate reductase (MTHFR), methylenetetrahydrofolate dehydrogenase, cyclohydrolase, and formyltetrahydrofolate synthetase 1 (MTHFD1), can cause HHcy and may also affect the efficacy of folic acid therapy. The details of mechanisms are yet to be further investigated. Method: We described a Chinese family with hereditary HHcy. The proband suffered from severe thromboembolic disease and experienced failure of folic acid therapy. Two sons of the proband were also diagnosed with HHcy but were sensitive to folic acid therapy. Whole-exome sequencing (WES) was conducted to evaluate the genetic lesion of this family. Results: Compound heterozygous variants (a common polymorphism, p. A222V, and a novel variant, p. C631*fs*1) of the MTHFR gene and a homozygous missense variant (p. K134R) of the MTHFD1 gene were identified in the proband. The two sons, with successful intervention, only harbored the homozygous p. A222V variant of the MTHFR gene. Conclusion: The clinical manifestations and genetic research synergistically confirmed the diagnosis of HHcy and clarified the failure of folic acid therapy in the proband caused by doubly bi-allelic variants of the MTHFR and MTHFD1 genes. Our study increased our understanding of the molecular basis of 1-CM-related gene defects on folic acid therapy in HHcy.

Novel compound heterozygous mutations of MTHFR Gene in a Chinese family with homocystinuria due to MTHFR deficiency

BACKGROUND

Homocystinuria due to methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare autosomal recessive disorder. The purpose of this study is to expand the mutation site of the MTHFR gene and provide genetic counseling for this family.

METHODS

A couple came to our hospital for pre-pregnancy genetic counseling. We collected the family history and detailed clinical information, then performed whole-exome sequencing, and analyzed the pathogenicity of the candidate mutations.

RESULTS

We found that the father of the proband had homocystinuria, the proband and his brother had low blood methionine levels at birth, and the brain MRI showed brain dysplasia. The third fetus was found to have a broadened triangle of the bilateral ventricle at 19 weeks of pregnancy. The compound heterozygous variants of c.602 A > C (p.His201Pro) and c.1316T > C (p.Leu439Pro) of the MTHFR gene in the first three fetuses were found by whole-exome sequencing. The heterozygous c.602 A > C variant of the MTHFR gene is a novel missense variant that has been submitted to the ClinVar with Variation ID 992,662.

CONCLUSION

In consideration of the clinical phenotype, family history, and result of genetic testing, we speculated that both patients may have homocystinuria due to MTHFR deficiency. Homocystinuria due to MTHFR deficiency caused by compound heterozygous mutations composed of the MTHFR gene in this family may be associated with cerebral atrophy and cerebral dysplasia. The novel compound heterozygous mutations broaden the mutation spectrum of the MTHFR gene and enhance the application of genetic counseling and carrier screening in rare diseases.

Association of methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms with vitamin B12 deficiency and adverse perinatal outcomes among pregnant women of rural South India - a cross sectional longitudinal study

OBJECTIVES

To determine the occurrence of MTHFR gene polymorphisms and to study their association with vitamin B12 deficiency and adverse perinatal outcomes among a cohort of pregnant women from Kaniyambadi block, Tamil Nadu.

METHODS

120 consecutive pregnant women who were ≤20 weeks of gestational age from the 82 villages of Kaniyambadi block were recruited. Genomic DNA was isolated from the peripheral blood. PCR amplification was done followed by Sangers sequencing. Maternal and neonatal outcomes were extracted. Data was entered and analysed.

RESULTS

Our study found the occurrence of c.1298A>C variant in homozygous state in 14.2% and c.677C>T heterozygous state in 15%. Sanger sequencing of exon 7 identified another pathogenic variant c.1262G>T in heterozygous state in two of them. Both the mothers who harboured that variant had preterm delivery and one of them gave birth to a low-birth-weight neonate. In the entire cohort, 5% of the mothers had abortion, 4.2% of them had preterm delivery and 8.8% of the neonates had low birth weight. Presence of c.1298A>C or c.677C>T variants were associated with vitamin B12 deficiency [Pearson Chi squared value (χ²)=7.9 and 7.6 respectively; p=0.02]. Heterozygous pathogenic variant c.1262G>T was associated with both adverse maternal [χ²=11.5; p=0.001] and neonatal [χ²=18.3; p=0.009] outcomes.

CONCLUSIONS

MTHFR gene polymorphisms could be associated with several adverse perinatal outcomes and vitamin B12 deficiency. Further larger studies are needed to prove the pathogenicity of c.1262G>T variant on pregnancy.

Evaluating the Association Between Genetic Polymorphisms Related to Homocysteine Metabolism and Unexplained Recurrent Pregnancy Loss in Women

Objective

To investigate the relationship between unexplained recurrent pregnancy loss (URPL) and polymorphisms of homocysteine metabolism-related genes in women.

Materials and Methods

A case-control study included 90 women with two or more consecutive unexplained pregnancy losses and 92 controlled women without miscarriage history; the female participants were in the age category of 18-35 years. The high-resolution melting technique was used to detect the single-nucleotide variants related to homocysteine metabolism disorder, namely MTHFR C677T, MTHFR A1298C, MTR A2756G, and MTRR A66G polymorphism.

Results

The MTHFR C677T polymorphism had significantly correlation with URPL. Indeed, the frequency of the677T allele and genotypes (677CT, 677TT) in the URPL group was significantly higher than that in the control group (p < 0.05). However, the allele, as well as genotype distribution of MTHFR A1298C, MTR A2756G, and MTRR A66G polymorphisms showed no significant difference (p > 0.05). MTHFR 677CT-1298AC genotype combination led to a 9.0-fold increased risk of URPL (OR 9.0; 95% CI, 2.25-35.99; p = 0.001), while the risk increased 10.0-fold (OR 10.0; 95% CI, 1.8-55.53; p = 0.008) when participants had more than the 3 variant loci.

Conclusion

The MTHFR C677T polymorphism was a risk factor for URPL, and determining the MTHFR C677T polymorphism had a potential prediction of URPL risk. Moreover, the MTHFR C677T and MTHFR A1298C joint mutants might have a synergistic effect on URPL. Conversely, there is a lack of evidence suggesting the URPL risk of MTHFR A1298C, MTR A2756G, and MTRR A66G polymorphisms.

Genetic origin of patients having spastic paraplegia with or without other neurologic manifestations

Background

Hereditary spastic paraplegia (HSP) is a group of neurodegenerative diseases characterized by lower-limb spastic paraplegia with highly genetic and clinical heterogeneity. However, the clinical sign of spastic paraplegia can also be seen in a variety of hereditary neurologic diseases with bilateral corticospinal tract impairment. The purpose of this study is to identify the disease spectrum of spastic paraplegia, and to broaden the coverage of genetic testing and recognize clinical, laboratorial, electrophysiological and radiological characteristics to increase the positive rate of diagnosis.

Methods

Twenty-seven cases were screened out to have definite or suspected pathogenic variants from clinically suspected HSP pedigrees through HSP-associated sequencing and/or expanded genetic testing. One case was performed for enzyme detection of leukodystrophy without next-generation sequencing. In addition, detailed clinical, laboratorial, electrophysiological and radiological characteristics of the 28 patients were presented.

Results

A total of five types of hereditary neurological disorders were identified in 28 patients, including HSP (15/28), leukodystrophy (5/28), hereditary ataxia (2/28), methylmalonic acidemia/methylenetetrahydrofolate reductase deficiency (5/28), and Charcot-Marie-tooth atrophy (1/28). Patients in the HSP group had chronic courses, most of whom were lower limbs spasticity, mainly with axonal neuropathy, and thinning corpus callosum, white matter lesions and cerebellar atrophy in brain MRI. In the non-HSP groups, upper and lower limbs both involvement was more common. Patients with homocysteine remethylation disorders or Krabbe’s disease or autosomal recessive spastic ataxia of Charlevoix-Saguenay had diagnostic results in laboratory or imaging examination. A total of 12 new variants were obtained.

Conclusions

HSP had widespread clinical and genetic heterogeneity, and leukodystrophy, hereditary ataxia, Charcot-Marie-Tooth atrophy and homocysteine remethylation disorders accounted for a significant proportion of the proposed HSP. These diseases had different characteristics in clinical, laboratorial, electrophysiological, and radiological aspects, which could help differential diagnosis. Genetic analysis could ultimately provide a clear diagnosis, and broadening the scope of genetic testing could improve the positive rate of diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02708-z.

Variable neurological phenotypes of homocystinuria caused by biallelic methylenetetrahydrofolate reductase variants

Inherited methylenetetrahydrofolate reductase (MTHFR) deficiency is associated with a wide spectrum of disorders including homocystinuria. This study aims to describe the neurological phenotypes and molecular profiles of patients with homocystinuria caused by biallelic variants in MTHFR. We report six subjects with MTHFR deficiency who presented with variable neurological phenotypes which could be viewed as a continuous spectrum. Fatal infantile encephalopathy was observed in one family, whereas another patient presented at 27 years with acute leukoencephalopathy and recovered within 3 months. Intermediate forms presenting as complicated hereditary spastic paraparesis of variable severity were observed in four subjects. Clinical and molecular information of the 207 cases reported in literature were also retrieved and analyzed. We categorized all subjects into three categories - severe, intermediate and mild forms according to the clinical presentation. In addition, a total of 286 disease-causing variations reported to date were analyzed. These included seven disease-causing variants reported in this study of which one is novel. Some genotype-phenotype correlation could be seen which corroborated with previous observations. However, inter- and intrafamilial variability was also noted. Treatment with betaine, B12 and folic acid was started in four subjects with variable outcomes.

Hydrocephalus presented as the prominent symptom of severe 5,10-methylenetetrahydrofolate reductase deficiency in an infant: A case report

Hyperhomocysteinemia is a common medical condition observed in patients with aminoaciduria. Deficiency in cystathionine beta-synthase, metabolism of cobalamin associated C, peroxiredoxin 1, 5-methyltetrahydrofolate-homocysteine methyltransferase reductase, LMBR1 domain containing 1, 5-methyltetrahydrofolate-homocysteine methyltransferase or 5,10-methylenetetrahydrofolate reductase (MTHFR) all can result in an elevation in plasma homocysteine, which has been reported to be a risk factor of vascular events, such as atherosis, acute myocardial infarction and cerebral stroke. Hyperhomocysteinemia due to the deficiency of 5,10-methylenetetrahydrofolate reductase (MTHFR; also known as 5,10-methyl THR reductase) is an autosomal recessive rare disease caused by defects in the MTHFR gene. The clinical manifestations of this disorder are heterogeneous, ranging from asymptomatic to severe neurological disorders. However, hydrocephalus has seldomly been reported in patients with MTHFR deficiency. The present study thus describes a case of severe MTHFR deficiency in an infant, whose main manifestation was hydrocephalus. The clinical course and genotype of the patient were also examined. Specifically, a 4-month-old boy with hydrocephalus was admitted to hospital. Clinical examinations and genetic sequencing of the patient were performed to determine the probable causative factors. A physical examination revealed that the patient had developmental delay and progressive hydrocephalus. Amino acid analysis of the blood revealed an enhancement in serum homocysteine levels and a decrease in blood methionine and free carnitine levels. The organic acid levels in urine were normal. Therefore, he was diagnosed with hyperhomocysteinemia. Targeted next-generation sequencing was performed to determine the pathogenetic gene in this case. A paternal mutation c.1530G>A (p.K510K) and a maternal mutation c.233C>A (p.S78X) were identified. Previous experimental evidence indicated that these two mutations were all pathogenic; therefore, this patient was ultimately diagnosed with MTHFR deficiency. The patient in described herein study presented with severe progressive hydrocephalus in association with a delayed developmental milestone. According to the clinical and genetic tests, the patient was diagnosed with severe MTHFR deficiency. It thus is recommended that screening for metabolites and performing gene sequencing in infants presenting with undisclosed hydrocephalus.

A Glance into MTHFR Deficiency at a Molecular Level

MTHFR deficiency still deserves an investigation to associate the phenotype to protein structure variations. To this aim, considering the MTHFR wild type protein structure, with a catalytic and a regulatory domain and taking advantage of state-of-the-art computational tools, we explore the properties of 72 missense variations known to be disease associated. By computing the thermodynamic ΔΔG change according to a consensus method that we recently introduced, we find that 61% of the disease-related variations destabilize the protein, are present both in the catalytic and regulatory domain and correspond to known biochemical deficiencies. The propensity of solvent accessible residues to be involved in protein-protein interaction sites indicates that most of the interacting residues are located in the regulatory domain, and that only three of them, located at the interface of the functional protein homodimer, are both disease-related and destabilizing. Finally, we compute the protein architecture with Hidden Markov Models, one from Pfam for the catalytic domain and the second computed in house for the regulatory domain. We show that patterns of disease-associated, physicochemical variation types, both in the catalytic and regulatory domains, are unique for the MTHFR deficiency when mapped into the protein architecture.

Exome-Wide Association Study Identifies East Asian-Specific Missense Variant MTHFR C136T Influencing Homocysteine Levels in Chinese Populations RH: ExWAS of tHCY in a Chinese Population

Plasma total homocysteine (tHCY) is a known risk factor of a wide range of complex diseases. No genome scans for tHCY have been conducted in East Asian populations. Here, we conducted an exome-wide association study (ExWAS) for tHCY in 5,175 individuals of Chinese Han origin, followed by a replication study in 668 Chinese individuals. The ExWAS identified two loci, 1p36.22 (lead single-nucleotide polymorphism (SNP) rs1801133, MTHFR C677T) and 16q24.3 (rs1126464, DPEP1), showing exome-wide significant association with tHCY (p < 5E-7); and both loci have been previously associated with tHCY in non-East Asian populations. Both SNPs were replicated in the replication study (p < 0.05). Conditioning on the genotype of C677T and rs1126464, we identified a novel East Asian-specific missense variant rs138189536 (C136T) of MTHFR (p = 6.53E-10), which was also significant in the replication study (p = 9.8E-3). The C136T and C677T variants affect tHCY in a compound heterozygote manner, where compound heterozygote and homozygote genotype carriers had on average 43.4% increased tHCY than had other genotypes. The frequency of the homozygote C677T genotype showed an inverse-U-shaped geospatial pattern globally with a pronounced frequency in northern China, which coincided with the high prevalence of hyperhomocysteinemia (HHCY) in northern China. A logistic regression model of HHCY status considering sex, age, and the genotypes of the three identified variants reached an area under the receiver operating characteristic curve (AUC) value of 0.74 in an independent validation cohort. These genetic observations provide new insights into the presence of multiple causal mutations at the MTHFR locus, highlight the role of genetics in HHCY epidemiology among different populations, and provide candidate loci for future functional studies.

Shifting landscapes of human MTHFR missense-variant effects

Most rare clinical missense variants cannot currently be classified as pathogenic or benign. Deficiency in human 5,10-methylenetetrahydrofolate reductase (MTHFR), the most common inherited disorder of folate metabolism, is caused primarily by rare missense variants. Further complicating variant interpretation, variant impacts often depend on environment. An important example of this phenomenon is the MTHFR variant p.Ala222Val (c.665C>T), which is carried by half of all humans and has a phenotypic impact that depends on dietary folate. Here we describe the results of 98,336 variant functional-impact assays, covering nearly all possible MTHFR amino acid substitutions in four folinate environments, each in the presence and absence of p.Ala222Val. The resulting atlas of MTHFR variant effects reveals many complex dependencies on both folinate and p.Ala222Val. MTHFR atlas scores can distinguish pathogenic from benign variants and, among individuals with severe MTHFR deficiency, correlate with age of disease onset. Providing a powerful tool for understanding structure-function relationships, the atlas suggests a role for a disordered loop in retaining cofactor at the active site and identifies variants that enable escape of inhibition by S-adenosylmethionine. Thus, a model based on eight MTHFR variant effect maps illustrates how shifting landscapes of environment- and genetic-background-dependent missense variation can inform our clinical, structural, and functional understanding of MTHFR deficiency.

Clinical and molecular characterization of adult patients with late-onset MTHFR deficiency

5,10-Methylenetetrahydrofolate reductase (MTHFR) deficiency usually presents as a severe neonatal disease. This study aimed to characterize natural history, biological and molecular data, and response to treatment of patients with late-onset MTHFR deficiency. The patients were identified through the European Network and Registry for Homocystinuria and Methylation Defects and the Adult group of the French Society for Inherited Metabolic Diseases; data were retrospectively colleted. To identify juvenile to adult-onset forms of the disease, we included patients with a diagnosis established after the age of 10 years. We included 14 patients (median age at diagnosis: 32 years; range: 11-54). At onset (median age: 20 years; range 9-38), they presented with walking difficulties (n = 8), cognitive decline (n = 3) and/or seizures (n = 3), sometimes associated with mild mental retardation (n = 6). During the disease course, symptoms were almost exclusively neurological with cognitive dysfunction (93%), gait disorders (86%), epilepsy (71%), psychiatric symptoms (57%), polyneuropathy (43%), and visual deficit (43%). Mean diagnostic delay was 14 years. Vascular events were observed in 28% and obesity in 36% of the patients. One patient remained asymptomatic at the age of 55 years. Upon treatment, median total homocysteine decreased (from 183 μmol/L, range 69-266, to 90 μmol/L, range 20-142) and symptoms improved (n = 9) or stabilized (n = 4). Missense pathogenic variants in the C-terminal regulatory domain of the protein were over-represented compared to early-onset cases. Residual MTHFR enzymatic activity in skin fibroblasts (n = 4) was rather high (17%-58%). This series of patients with late-onset MTHFR deficiency underlines the still unmet need of a prompt diagnosis of this treatable disease.

Identification of small molecule allosteric modulators of 5,10-methylenetetrahydrofolate reductase (MTHFR) by targeting its unique regulatory domain

The folate and methionine cycles, constituting one-carbon metabolism, are critical pathways for cell survival. Intersecting these two cycles, 5,10-methylenetetrahydrofolate reductase (MTHFR) directs one-carbon units from the folate to methionine cycle, to be exclusively used for methionine and S-adenosylmethionine (AdoMet) synthesis. MTHFR deficiency and upregulation result in diverse disease states, rendering it an attractive drug target. The activity of MTHFR is inhibited by the binding of AdoMet to an allosteric regulatory domain distal to the enzyme's active site, which we have previously identified to constitute a novel fold with a druggable pocket. Here, we screened 162 AdoMet mimetics using differential scanning fluorimetry, and identified 4 compounds that stabilized this regulatory domain. Three compounds were sinefungin analogues, closely related to AdoMet and S-adenosylhomocysteine (AdoHcy). The strongest thermal stabilisation was provided by (S)-SKI-72, a potent inhibitor originally developed for protein arginine methyltransferase 4 (PRMT4). Using surface plasmon resonance, we confirmed that (S)-SKI-72 binds MTHFR via its allosteric domain with nanomolar affinity. Assay of MTHFR activity in the presence of (S)-SKI-72 demonstrates inhibition of purified enzyme with sub-micromolar potency and endogenous MTHFR from HEK293 cell lysate in the low micromolar range, both of which are lower than AdoMet. Nevertheless, unlike AdoMet, (S)-SKI-72 is unable to completely abolish MTHFR activity, even at very high concentrations. Combining binding assays, kinetic characterization and compound docking, this work indicates the regulatory domain of MTHFR can be targeted by small molecules and presents (S)-SKI-72 as an excellent candidate for development of MTHFR inhibitors.

Rare variants in MTHFR predispose to occurrence and recurrence of pulmonary embolism

BACKGROUND

Rare genetic variants play a critical role in unprovoked pulmonary embolism (PE). However, the known risk genes only account a small proportion of patients with PE. The objective of this study was to investigate the relationship between the rare variants of gene encoding methylenetetrahydrofolate reductase (MTHFR) and the initiation and long-term clinical outcomes of PE.

METHODS

The rare variants of MTHFR were detected by whole exome sequencing of DNA from 258 unprovoked PE cases and 11,451 controls. Correlation of genotype and clinical phenotype and outcome were evaluated at baseline and after follow-up.

RESULTS

MTHFR rare variants were found in 15 of 258 cases (5.81%) and 241 of 11,451 controls (2.10%), conferring 2.87-fold greater odds of the PE occurrence (OR = 2.87, 95% CI = 1.68-4.91, P = 5.6 × 10^-5, chi-square test). The patients with MTHFR rare variants had higher plasma level of homocysteine than those without. During a follow-up of 3.0 years, a total of 84 events were identified. The recurrent PE (two or more events of PE) were significantly higher in patients carrying MTHFR rare variants (8/15, 53.3%) compared with those without (55/239, 23.0%) (P = 0.023).

CONCLUSION

We speculate that MTHFR rare variants may increase the occurrence and recurrence of PE.

The 1316T>C missenses mutation in MTHFR contributes to MTHFR deficiency by targeting MTHFR to proteasome degradation

5,10-methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare hereditary disease characterized by defects in folate and homocysteine metabolism. Individuals with inherited MTHFR gene mutations have a higher tendency to develop neurodegeneration disease as Alzheimer’ disease and atherosclerosis. MTHFR is a rate-limiting enzyme catalyzing folate production, various SNPs/mutations in the MTHFR gene have been correlated to MTHFR deficiency. However, the molecular mechanisms underpinning the pathogenic effects of these SNPs/mutations have not been clearly understood. In the present study, we reported a severe MTHFR deficiency patient with late-onset motor dysfunction and sequenced MTHFR gene exons of the family. The patient carries an MD-associating SNP (rs748289202) in one MTHFR allele and the rs545086633 SNP with unknown disease relevance in the other. The rs545086633 SNP (p.Leu439Pro) results in an L439P substitution in MTHFR protein, and drastically decreases mutant protein expression by promoting proteasomal degradation. L⁴³⁹ in MTHFR is highly conserved in vertebrates. Our study demonstrated that p.Leu439Pro in MTHFR is the first mutation causing significant intracellular defects of MTHFR, and rs545086633 should be examined for the in-depth diagnosis and treatment of MD.

Allosteric inhibition of MTHFR prevents futile SAM cycling and maintains nucleotide pools in one-carbon metabolism

Methylenetetrahydrofolate reductase (MTHFR) links the folate cycle to the methionine cycle in one-carbon metabolism. The enzyme is known to be allosterically inhibited by SAM for decades, but the importance of this regulatory control to one-carbon metabolism has never been adequately understood. To shed light on this issue, we exchanged selected amino acid residues in a highly conserved stretch within the regulatory region of yeast MTHFR to create a series of feedback-insensitive, deregulated mutants. These were exploited to investigate the impact of defective allosteric regulation on one-carbon metabolism. We observed a strong growth defect in the presence of methionine. Biochemical and metabolite analysis revealed that both the folate and methionine cycles were affected in these mutants, as was the transsulfuration pathway, leading also to a disruption in redox homeostasis. The major consequences, however, appeared to be in the depletion of nucleotides. 13C isotope labeling and metabolic studies revealed that the deregulated MTHFR cells undergo continuous transmethylation of homocysteine by methyltetrahydrofolate (CH3THF) to form methionine. This reaction also drives SAM formation and further depletes ATP reserves. SAM was then cycled back to methionine, leading to futile cycles of SAM synthesis and recycling and explaining the necessity for MTHFR to be regulated by SAM. The study has yielded valuable new insights into the regulation of one-carbon metabolism, and the mutants appear as powerful new tools to further dissect out the intersection of one-carbon metabolism with various pathways both in yeasts and in humans.

Hyperhomocysteinemia: Clinical Insights

Homocysteine (Hcy) is a sulfhydryl-containing amino acid, and intermediate metabolite formed in metabolising methionine (Met) to cysteine (Cys); defective Met metabolism can increase Hcy. The effect of hyperhomocysteinemia (HHcy) on human health, is well described and associated with multiple clinical conditions. HHcy is considered to be an independent risk factor for common cardiovascular and central nervous disorders, where its role in folate metabolism and choline catabolism is fundamental in many metabolic pathways. HHcy induces inflammatory responses via increasing the pro-inflammatory cytokines and downregulation of anti-inflammatory cytokines which lead to Hcy-induced cell apoptosis. Conflicting evidence indicates that the development of the homocysteine-associated cerebrovascular disease may be prevented by the maintenance of normal Hcy levels. In this review, we discuss common conditions associated with HHcy and biochemical diagnostic workup that may help in reaching diagnosis at early stages. Furthermore, future systematic studies need to prove the exact pathophysiological mechanism of HHcy at the cellular level and the effect of Hcy lowering agents on disease courses.

Adolescent/adult-onset homocysteine remethylation disorders characterized by gait disturbance with/without psychiatric symptoms and cognitive decline: a series of seven cases

Homocysteine remethylation disorders are rare inherited disorders caused by a deficient activity of the enzymes involved in the remethylation of homocysteine to methionine. The adolescent/adult-onset remethylation disorders are rarely reported. We analyzed the clinical and genetic characteristics of seven cases with adolescent/adult remethylation disorders, including 5 cases of the cobalamin C disease (cblC) and 2 cases of the methylenetetrahydrofolate reductase deficiency. The average onset age was 21.1 (range 14 to 40) years. All patients complained of gait disturbances. Other common symptoms included psychiatric symptoms (5/7) and cognitive decline (4/7). Acute encephalopathy, dysarthria, anorexia, vomiting, ketoacidosis, anemia, cataract, and hand tremor were also observed. The mean total homocysteine in serum when the patients were diagnosed was 94.6 (range 53.1-154.5) mol/L. Electrophysiological studies revealed neuropathy in the lower limbs (6/7). The brain MRI showed reversible altered signal from the dorsal portions of the cerebellar hemispheres (1/7), periventricular hyperintensity (2/7), and delayed/impaired myelination (2/7). The sural nerve biopsy performed in one case showed a modest loss of myelinated fibers. Five patients showed heterozygous mutations of the MMACHC gene, including c.482G>A (5/5), c.609G>A (2/5), and c.658-660delAAG (3/5). Two patients showed heterozygous mutations of the MTHFR gene, including c.698C>A (2/2), c.698C>G (1/2), and c.236+1G>A (1/2). The patients responded well to the treatments with significant improvements. Adolescent/adult-onset remethylation disorders are easily misdiagnosed. We recommend testing the serum homocysteine concentrations in young/adult patients with unexplained neuro-psychotic symptoms. Furthermore, individuals with significantly elevated serum homocysteine concentrations should be further tested by organic acid screening and genetic analysis.

Cerebral folate deficiency: Analytical tests and differential diagnosis

Cerebral folate deficiency is typically defined as a deficiency of the major folate species 5-methyltetrahydrofolate in the cerebrospinal fluid (CSF) in the presence of normal peripheral total folate levels. However, it should be noted that cerebral folate deficiency is also often used to describe conditions where CSF 5-MTHF is low, in the presence of low or undefined peripheral folate levels. Known defects of folate transport are deficiency of the proton coupled folate transporter, associated with systemic as well as cerebral folate deficiency, and deficiency of the folate receptor alpha, leading to an isolated cerebral folate deficiency associated with intractable seizures, developmental delay and/or regression, progressive ataxia and choreoathetoid movement disorders. Inborn errors of folate metabolism include deficiencies of the enzymes methylenetetrahydrofolate reductase, dihydrofolate reductase and 5,10-methenyltetrahydrofolate synthetase. Cerebral folate deficiency is potentially a treatable condition and so prompt recognition of these inborn errors and initiation of appropriate therapy is of paramount importance. Secondary cerebral folate deficiency may be observed in other inherited metabolic diseases, including disorders of the mitochondrial oxidative phosphorylation system, serine deficiency, and pyridoxine dependent epilepsy. Other secondary causes of cerebral folate deficiency include the effects of drugs, immune response activation, toxic insults and oxidative stress. This review describes the absorption, transport and metabolism of folate within the body; analytical methods to measure folate species in blood, plasma and CSF; inherited and acquired causes of cerebral folate deficiency; and possible treatment options in those patients found to have cerebral folate deficiency.

A Novel Homozygous Non-sense Mutation in the Catalytic Domain of MTHFR Causes Severe 5,10-Methylenetetrahydrofolate Reductase Deficiency

Background: Severe 5,10-methylenetetrahydrofolate reductase (MTHFR) deficiency is a heterogeneous metabolic disorder inherited in an autosomal recessive manner. Pathogenic mutations in MTHFR gene have been associated with severe MTHFR deficiency. The clinical presentation of MTHFR deficiency is highly variable and associated with several neurological anomalies. Methods: Direct whole-exome sequencing (WES) was performed in all the five available individuals from the family, including the affected individual (III-7) using standard procedures. Results: We observed a proband (III-7) with an abnormality in the cerebral white matter, apnoea, and microcephaly. WES analysis identified a novel homozygous non-sense mutation (c.154C>T; p.Arg52^*) in MTHFR gene that segregated with the disease phenotype within the family. Conclusion: We identified a novel non-sense mutation in MTHFR gene in a single Egyptian family with severe MTHFR deficiency. The present investigation is clinically important, as it adds to the growing list of MTHFR mutations, which might help in genetic counseling of families of affected children and proper genotype-phenotype correlation.

Estimating carrier frequencies of newborn screening disorders using a whole-genome reference panel of 3552 Japanese individuals

Incidence rates of Mendelian diseases vary among ethnic groups, and frequencies of variant types of causative genes also vary among human populations. In this study, we examined to what extent we can predict population frequencies of recessive disorders from genomic data, and explored better strategies for variant interpretation and classification. We used a whole-genome reference panel from 3552 general Japanese individuals constructed by the Tohoku Medical Megabank Organization (ToMMo). Focusing on 32 genes for 17 congenital metabolic disorders included in newborn screening (NBS) in Japan, we identified reported and predicted pathogenic variants through variant annotation, interpretation, and multiple ways of classifications. The estimated carrier frequencies were compared with those from the Japanese NBS data based on 1,949,987 newborns from a previous study. The estimated carrier frequency based on genomic data with a recent guideline of variant interpretation for the PAH gene, in which defects cause hyperphenylalaninemia (HPA) and phenylketonuria (PKU), provided a closer estimate to that by the observed incidence than the other methods. In contrast, the estimated carrier frequencies for SLC25A13, which causes citrin deficiency, were much higher compared with the incidence rate. The results varied greatly among the 11 NBS diseases with single responsible genes; the possible reasons for departures from the carrier frequencies by reported incidence rates were discussed. Of note, (1) the number of pathogenic variants increases by including additional lines of evidence, (2) common variants with mild effects also contribute to the actual frequency of patients, and (3) penetrance of each variant remains unclear.

Computational modelling folate metabolism and DNA methylation: implications for understanding health and ageing

Dietary folates have a key role to play in health, as deficiencies in the intake of these B vitamins have been implicated in a wide variety of clinical conditions. The reason for this is folates function as single carbon donors in the synthesis of methionine and nucleotides. Moreover, folates have a vital role to play in the epigenetics of mammalian cells by supplying methyl groups for DNA methylation reactions. Intriguingly, a growing body of experimental evidence suggests that DNA methylation status could be a central modulator of the ageing process. This has important health implications because the methylation status of the human genome could be used to infer age-related disease risk. Thus, it is imperative we further our understanding of the processes which underpin DNA methylation and how these intersect with folate metabolism and ageing. The biochemical and molecular mechanisms, which underpin these processes, are complex. However, computational modelling offers an ideal framework for handling this complexity. A number of computational models have been assembled over the years, but to date, no model has represented the full scope of the interaction between the folate cycle and the reactions, which governs the DNA methylation cycle. In this review, we will discuss several of the models, which have been developed to represent these systems. In addition, we will present a rationale for developing a combined model of folate metabolism and the DNA methylation cycle.

Psychiatric Disorders Secondary to Neurometabolic Disorders

Some diseases secondary to inborn errors of metabolism are associated with psychiatric disorders or minor neurological symptoms. The existence of some cases with exclusively psychiatric symptoms represents a diagnostic and therapeutic challenge. The aim of this article is to describe seven treatable neurometabolic disorders that should be taken into account in the psychiatric consultation as they manifest with psychiatric symptoms that mask the organic origin of the disorder. Homocysteine metabolism and urea cycle disorders, Wilson's disease, Niemann-Pick disease Type C, acute porphyria and cerebrotendinous xanthomatosis are described. Following an analysis of the literature, a list of psychiatric symptoms associated with these disorders are proposed, ranging from insidious changes in affective state and thought to atypical symptoms such as visual hallucinations, as well as paradoxical effects of antipsychotics or behavioural disorders in children and adolescents associated with loss of autonomy. The most frequently associated neurological signs, such as alterations in the state of consciousness, motor behaviour and balance disorders, catatonia or progressive cognitive deficit are also listed. Emphasis is placed on the importance of considering resistance to antipsychotic treatment as a warning sign to suspect organicity, as well as the significant improvement in psychiatric impairment when effective and early treatment is established.

Structural basis for the regulation of human 5,10-methylenetetrahydrofolate reductase by phosphorylation and S-adenosylmethionine inhibition

The folate and methionine cycles are crucial for biosynthesis of lipids, nucleotides and proteins, and production of the methyl donor S-adenosylmethionine (SAM). 5,10-methylenetetrahydrofolate reductase (MTHFR) represents a key regulatory connection between these cycles, generating 5-methyltetrahydrofolate for initiation of the methionine cycle, and undergoing allosteric inhibition by its end product SAM. Our 2.5 Å resolution crystal structure of human MTHFR reveals a unique architecture, appending the well-conserved catalytic TIM-barrel to a eukaryote-only SAM-binding domain. The latter domain of novel fold provides the predominant interface for MTHFR homo-dimerization, positioning the N-terminal serine-rich phosphorylation region near the C-terminal SAM-binding domain. This explains how MTHFR phosphorylation, identified on 11 N-terminal residues (16 in total), increases sensitivity to SAM binding and inhibition. Finally, we demonstrate that the 25-amino-acid inter-domain linker enables conformational plasticity and propose it to be a key mediator of SAM regulation. Together, these results provide insight into the molecular regulation of MTHFR.

The human enzyme MTHFR links the folate and methionine cycles, which are essential for the biosynthesis of nucleotides and proteins. Here, the authors present the crystal structure and biochemical analysis of human MTHFR, providing molecular insights into its function and regulation in higher eukaryotes.

The genetic component of preeclampsia: A whole-exome sequencing study

Preeclampsia is a major cause of maternal and perinatal deaths. The aetiology of preeclampsia is largely unknown but a polygenetic component is assumed. To explore this hypothesis, we performed an in-depth whole-exome sequencing study in women with (cases, N = 50) and without (controls, N = 50) preeclampsia. The women were identified in an unselected cohort of 2,545 pregnant women based on data from the Danish National Patient Registry and the Medical Birth Registry. Matching DNA was obtained from a biobank containing excess blood from routine antenatal care visits. Novogene performed the whole-exome sequencing blinded to preeclampsia status. Variants for comparison between cases and controls were filtered in the Ingenuity Variant Analysis software. We applied two different strategies; a disease association panel approach, which included variants in single genes associated with established clinical risk factors for preeclampsia, and a gene panel approach, which included biological pathways harbouring genes previously reported to be associated with preeclampsia. Variant variability was compared in cases and controls at the level of biological processes, signalling pathways, and in single genes. Regardless of the applied strategy and the level of variability examined, we consistently found positive correlations between variant numbers in cases and controls (all R²s>0.88). Contrary to what was expected, cases carried fewer variants in biological processes and signalling pathways than controls (all p-values ≤0.02). In conclusion, our findings challenge the hypothesis of a polygenetic aetiology for preeclampsia with a common network of susceptibility genes. The greater genetic diversity among controls may suggest a protective role of genetic diversity against the development of preeclampsia.

Association Study of Polymorphisms in Genes Relevant to Vitamin B12 and Folate Metabolism with Childhood Autism Spectrum Disorder in a Han Chinese Population

Background

Both genetic and environmental factors play a role in the development of autism spectrum disorder (ASD). This case-control study examined the association between childhood ASD and single-nucleotide polymorphisms (SNPs) in genes involved with vitamin B12 and folate metabolism.

Material/Methods

Genotypes of transcobalamin 2 (TCN2) rs1801198, methionine synthase (MTR) rs1805087, methionine synthase reductase (MTRR) rs1801394, and methylene tetrahydrofolate reductase (MTHFR) rs1801133 were examined in 201 children with ASD and 200 healthy controls from the Han Chinese population.

Results

Our results showed no association of all examined SNPs with childhood ASD and its severity.

Conclusions

None of the examined SNPs were a risk factor for the susceptibility to childhood ASD and severity of the disease in a Han Chinese population.

Role of folate in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of chronic liver conditions that are characterized by steatosis, inflammation, fibrosis, and liver injury. The global prevalence of NAFLD is rapidly increasing in proportion to the rising incidence of obesity and type 2 diabetes. Because NAFLD is a multifaceted disorder with many underlying metabolic abnormalities, currently, there is no pharmacological agent that is therapeutically approved for the treatment of this disease. Folate is a water-soluble B vitamin that plays an essential role in one-carbon transfer reactions involved in nucleic acid biosynthesis, methylation reactions, and sulfur-containing amino acid metabolism. The liver is the primary organ responsible for storage and metabolism of folates. Low serum folate levels have been observed in patients with obesity and diabetes. It has been reported that a low level of endogenous folates in rodents perturbs folate-dependent one-carbon metabolism, and may be associated with development of metabolic diseases such as NAFLD. This review highlights the biological role of folate in the progression of NAFLD and its associated metabolic complications including obesity and type 2 diabetes. Understanding the role of folate in metabolic disease may position this vitamin as a potential therapeutic for NAFLD.

Functional characterization of missense mutations in severe methylenetetrahydrofolate reductase deficiency using a human expression system

5,10-Methylenetetrahydrofolate reductase (MTHFR) catalyzes the NADPH-dependent reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate using FAD as the cofactor. Severe MTHFR deficiency is the most common inborn error of folate metabolism, resulting in hyperhomocysteinemia and homocystinuria. Approximately 70 missense mutations have been described that cause severe MTHFR deficiency, however, in most cases their mechanism of dysfunction remains unclear. Few studies have investigated mutational specific defects; most of these assessing only activity levels from a handful of mutations using heterologous expression. Here, we report the in vitro expression of 22 severe MTHFR missense mutations and two known single nucleotide polymorphisms (p.Ala222Val, p.Thr653Met) in human fibroblasts. Significant reduction of MTHFR activity (<20 % of wild-type) was observed for five mutant proteins that also had highly reduced protein levels on Western blot analysis. The remaining mutations produced a spectrum of enzyme activity levels ranging from 22-122 % of wild-type, while the SNPs retained wild-type-like activity levels. We found increased thermolability for p.Ala222Val and seven disease-causing mutations all located in the catalytic domain, three of which also showed FAD responsiveness in vitro. By contrast, six regulatory domain mutations and two mutations clustering around the linker region showed increased thermostability compared to wild-type protein. Finally, we confirmed decreased affinity for NADPH in individual mutant enzymes, a result previously described in primary patient fibroblasts. Our expression study allows determination of significance of missense mutations in causing deleterious loss of MTHFR protein and activity, and is valuable in detection of aberrant kinetic parameters, but should not replace investigations in native material.

Synthetic combinations of missense polymorphic genetic changes underlying Down syndrome susceptibility

Single nucleotide polymorphisms (SNPs) are important biomolecular markers in health and disease. Down syndrome, or Trisomy 21, is the most frequently occurring chromosomal abnormality in live-born children. Here, we highlight associations between SNPs in several important enzymes involved in the one-carbon folate metabolic pathway and the elevated maternal risk of having a child with Down syndrome. Our survey highlights that the combination of SNPs may be a more reliable predictor of the Down syndrome phenotype than single SNPs alone. We also describe recent links between SNPs in p53 and its related pathway proteins and Down syndrome, as well as highlight several proteins that help to associate apoptosis and p53 signaling with the Down syndrome phenotype. In addition to a comprehensive review of the literature, we also demonstrate that several SNPs reside within the same regions as these Down syndrome-linked SNPs, and propose that these closely located nucleotide changes may provide new candidates for future exploration.