Life-threatening methylenetetrahydrofolate reductase (MTHFR) deficiency with extremely early onset: characterization of two novel mutations in compound heterozygous patients

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.

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.

Hypoventilation and progressive encephalopathy in a neonate with MTHFR deficiency

Methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare autosomal recessive inherited inborn error of metabolism, which presents with various severity depending on the level of residual enzyme activity. In neonates, it can present with recurrent hypoventilation episodes, persistent encephalopathy with or without microcephaly. MTHFR deficiency also results in hyperhomocysteinemia, homocystinuria and hypomethionemia. We report a male neonate with severe MTHFR deficiency presenting to us on third week of life with progressive encephalopathy, microcephaly, seizures, central hypoventilation. There was similar history in the previous sibling. The patient's blood lactate, ammonia, tandem mass spectrometry for amino acids and acyl carnitine were normal. He remained encephalopathic with progressive increase in need of respiratory support in spite of supportive treatment and metabolic cocktail consisting of riboflavin, pyridoxine, coenzyme Q and carnitine. This neonate had novel homozygous mutation, which results in MTHFR deficiency. In newborn with hypoventilation or recurrent apnoea with encephalopathy and microcephaly, MTHFR deficiency should be considered as a differential diagnosis. Mutation study helps in confirming diagnosis; however, extended newborn metabolic screening with homocysteine level could help in early diagnosis of these cases.

Association of three missense mutations in the homocysteine-related MTHFR and MTRR gene with risk of polycystic ovary syndrome in Southern Chinese women

BACKGROUND

The etiology between homocysteine and polycystic ovary syndrome (PCOS) is unclear. In humans, the level of homocysteine is mainly affected by two enzymes: methylene tetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR). While the activity of these two enzymes is mainly affected by three missense mutations, namely C677T (MTHFR), A1298C (MTHFR), and A66G (MTRR). This study aims to examine the association between the three missense mutations and PCOS and investigate whether the three missense mutations exerted their effect on PCOS by affecting the homocysteine level.

METHODS

A case-control study was designed, comprising 150 people with PCOS and 300 controls. Logistic regression analysis was used to assess the association between the three missense mutations and PCOS. Linear regression analysis was used to assess the association between the three missense mutations and the homocysteine level. Mediation analysis was used to investigate whether the three missense mutations exerted their effect on PCOS by affecting the homocysteine level.

RESULTS

Following adjustments and multiple rounds of testing, MTHFR A1298C was found to be significantly associated with PCOS in a dose-dependent manner (compared to AA, OR = 2.142 for AC & OR = 3.755 for CC; P < 0.001). MTRR A66G was nominally associated with PCOS. Mutations in MTHFR A1298C and MTRR A66G were significantly associated with the homocysteine level. Mediation analysis suggested the effect of MTHFR A1298C on PCOS was mediated by homocysteine.

CONCLUSIONS

MTHFR A1298C and MTRR A66G were associated with PCOS, and MTHFR A1298C might affect the risk of PCOS by influencing the homocysteine level.

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.

Mutations in MTHFR and POLG impaired activity of the mitochondrial respiratory chain in 46-year-old twins with spastic paraparesis

Hereditary spastic paraplegias (HSPs) are characterized by lower extremity spasticity and weakness. HSP is often caused by mutations in SPG genes, but it may also be produced by inborn errors of metabolism. We performed next-generation sequencing of 4813 genes in one adult twin pair with HSP and severe muscular weakness occurring at the same age. We found two pathogenic compound heterozygous variants in MTHFR, including a variant not referenced in international databases, c.197C>T (p.Pro66Leu) and a known variant, c.470G>A (p.Arg157Gln), and two heterozygous pathogenic variants in POLG, c.1760C>T (p.Pro587Leu) and c.752C>T (p.Thr251Ile). MTHFR and POLG mutations were consistent with the severe muscle weakness and the metabolic changes, including hyperhomocysteinemia and decreased activity of both N(5,10)methylenetetrahydrofolate reductase (MTHFR) and complexes I and II of the mitochondrial respiratory chain. These data suggest the potential role of MTHFR and POLG mutations through consequences on mitochondrial dysfunction in the occurrence of spastic paraparesis phenotype with combined metabolic, muscular, and neurological components.

C677T polymorphism increases the risk of early spontaneous abortion

Purpose

To investigate the relationship of the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism in male population having spouses with early spontaneous abortion.

Methods

A total of 345 males whose spouses had at least one early spontaneous abortion were included in the study group, and 145 males who planned to have a second child were included in the control group. Semen was collected in a sterile cup by masturbation. After liquefaction, the sperm concentration and forward motility sperm rate (PR) were obtained. The genomic DNA was extracted from peripheral vein, followed by MTHFR C677T polymorphism detection through PCR-gold magnetic nanoparticle chromatography.

Results

The numbers of alleles and genotypes of MTHFR in the case group were 303 (C), 387 (T), 64 (CC), 175 (CT), and 106 (TT) cases, respectively. The numbers of allele and genotype of MTHFR in the control group were 167 (C), 123 (T), 145 (CC), 65 (CT), and 29 (TT) cases. There were significant differences in the distribution frequency of genotypes (χ² = 17.005, P = 0.000) and alleles (χ² = 15.295, P = 0.000) between the two groups. For cases with more spontaneous abortion, more cases had CT and TT phenotypes. Participants with genotype CT had the highest sperm concentration and PR in both groups (P < 0.05).

Conclusions

MTHFR could affect sperm DNA integrity through affecting DNA methylation, which led to an increase in the rate of early spontaneous abortion in spouses.

Electronic supplementary material

The online version of this article (10.1007/s10815-019-01500-2) contains supplementary material, which is available to authorized users.

Clinical pattern, mutations and in vitro residual activity in 33 patients with severe 5, 10 methylenetetrahydrofolate reductase (MTHFR) deficiency

BACKGROUND

Severe methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare inborn defect disturbing the remethylation of homocysteine to methionine (<200 reported cases). This retrospective study evaluates clinical, biochemical genetic and in vitro enzymatic data in a cohort of 33 patients.

METHODS

Clinical, biochemical and treatment data was obtained from physicians by using a questionnaire. MTHFR activity was measured in primary fibroblasts; genomic DNA was extracted from cultured fibroblasts.

RESULTS

Thirty-three patients (mean age at follow-up 11.4 years; four deceased; median age at first presentation 5 weeks; 17 females) were included. Patients with very low (<1.5%) mean control values of enzyme activity (n = 14) presented earlier and with a pattern of feeding problems, encephalopathy, muscular hypotonia, neurocognitive impairment, apnoea, hydrocephalus, microcephaly and epilepsy. Patients with higher (>1.7-34.8%) residual enzyme activity had mainly psychiatric symptoms, mental retardation, myelopathy, ataxia and spasticity. Treatment with various combinations of betaine, methionine, folate and cobalamin improved the biochemical and clinical phenotype. During the disease course, patients with very low enzyme activity showed a progression of feeding problems, neurological symptoms, mental retardation, and psychiatric disease while in patients with higher residual enzyme activity, myelopathy, ataxia and spasticity increased. All other symptoms remained stable or improved in both groups upon treatment as did brain imaging in some cases. No clear genotype-phenotype correlation was obvious.

DISCUSSION

MTHFR deficiency is a severe disease primarily affecting the central nervous system. Age at presentation and clinical pattern are correlated with residual enzyme activity. Treatment alleviates biochemical abnormalities and clinical symptoms partially.

Outcomes of four patients with homocysteine remethylation disorders detected by newborn screening

PURPOSE

We evaluated the clinical outcome in homocysteine remethylation disorders following newborn screening (NBS) and initiation of early specific treatment.

METHODS

Five patients with remethylation disorders were included in this study.

RESULTS

Two asymptomatic patients (one with cblG and one with cblE) were identified by NBS using an approach that combines a postanalytical interpretive tool (available on the Region 4 Stork (R4S) collaborative project website, http://www.clir-r4s.org) and a second-tier test for total homocysteine determination. Both the initial screening and the second-tier test are performed on the same blood spot, with no additional patient contact, resulting in no false-positive outcomes. Two additional patients with methylenetetrahydrofolate reductase deficiency were detected by NBS using low methionine as a marker. Although already symptomatic despite the early diagnosis, the latter two patients greatly improved with treatment and their outcomes are compared with that of another patient with methylenetetrahydrofolate reductase deficiency and significant morbidity who was diagnosed clinically at 3 months of age.

CONCLUSION

Early detection by NBS and timely and specific treatment considerably improve at least short-term outcomes of homocysteine remethylation disorders. When a remethylation disorder is suspected, group-specific treatment could be started prior to the completion of in vitro confirmatory testing because all disorders from this group require similar intervention.

Congenital MTHFR deficiency causing early-onset cerebral stroke in a case homozygous for MTHFR thermolabile variant

Hyperhomocysteinemia is a risk factor for early-onset venous thrombosis. It can be caused by genetic defects in methionine-homocysteine metabolism. The thermolabile variant of methylene-tetrahydrofolate reductase (MTHFR), c.677C>T, is one of the most common genetic condition, which has been associated with mild to moderate hyperhomocysteinemia, and carriers of this variant are at increased risk of an early-onset stroke-like episode. However, congenital MTHFR deficiency is a rare inborn error of folate metabolism, causing marked hyperhomocysteinemia, and its combination with the thermolabile variant is rarely reported. In this report, we describe a young adult with cerebral infarction. The patient was homozygous for the MTHFR thermolabile variant, but markedly elevated hyperhomocysteinemia led us to investigate the whole MTHFR gene, which revealed two novel MTHFR mutations. This is the first report of MTHFR deficiency in a Korean patient, and one of only a few cases reported in East Asian countries. Despite its rarity, our report underlines the importance of its identification in hyperhomocysteinemia for patient prognosis with appropriate management.

Flavin-dependent enzymes in cancer prevention

Statistical studies have demonstrated that various agents may reduce the risk of cancer's development. One of them is activity of flavin-dependent enzymes such as flavin-containing monooxygenase (FMO)(GS-OX1), FAD-dependent 5,10-methylenetetrahydrofolate reductase and flavin-dependent monoamine oxidase. In the last decade, many papers concerning their structure, reaction mechanism and role in the cancer prevention were published. In our work, we provide a more in-depth analysis of flavin-dependent enzymes and their contribution to the cancer prevention. We present the actual knowledge about the glucosinolate synthesized by flavin-containing monooxygenase (FMO)(GS-OX1) and its role in cancer prevention, discuss the influence of mutations in FAD-dependent 5,10-methylenetetrahydrofolate reductase on the cancer risk, and describe FAD as an important cofactor for the demethylation of histons. We also present our views on the role of riboflavin supplements in the prevention against cancer.

Metabolic and monogenic causes of seizures in neonates and young infants

Seizures in neonates or young infants present a frequent diagnostic challenge. After exclusion of acquired causes, disturbances of the internal homeostasis and brain malformations, the physician must evaluate for inborn errors of metabolism and for other non-malformative genetic disorders as the cause of seizures. The metabolic causes can be categorized into disorders of neurotransmitter metabolism, disorders of energy production, and synthetic or catabolic disorders associated with brain malformation, dysfunction and degeneration. Other genetic conditions involve channelopathies, and disorders resulting in abnormal growth, differentiation and formation of neuronal populations. These conditions are important given their potential for treatment and the risk for recurrence in the family. In this paper, we will succinctly review the metabolic and genetic non-malformative causes of seizures in neonates and infants less than 6 months of age. We will then provide differential diagnostic clues and a practical paradigm for their evaluation.