Severe Methylenetetrahydrofolate Reductase (MTHFR) Deficiency: A Case Report of Nonclassical Homocystinuria
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Severe methylenetetrahydrofolate reductase deficiency is an autosomal recessive metabolic disorder of folate metabolism causing elevated plasma homocysteine levels and homocystinuria (MIM 236250). A developmentally delayed 10-year-old girl presented with symptoms of progressive ataxia, dysarthria, tremor, mental status changes, and white-matter changes on magnetic resonance imaging. These changes occurred during a 3- to 4-month time period, with an acceleration of symptoms during 2 to 3 weeks. The patient was found to have extremely high serum homocysteine and low—normal serum methionine. She received treatment with vitamin B12, folate, betaine, multivitamins, and aspirin, with subsequent improvement of her symptoms and reduction in her serum homocysteine level. This case emphasizes the need to include homocystinuria in the differential diagnosis of children with acute/subacute neurological changes, particularly in the context of developmental delay.Keywords:
Homocystinuria
MTHFR (methylenetetrahydrofolate reductase) catalyses the synthesis of 5-methyltetrahydrofolate, the folate derivative utilized in homocysteine remethylation to methionine. A severe deficiency of MTHFR results in hyperhomocysteinaemia and homocystinuria. Betaine supplementation has proven effective in ameliorating the biochemical abnormalities and the clinical course in patients with this deficiency. Mice with a complete knockout of MTHFR serve as a good animal model for homocystinuria; early postnatal death of these mice is common, as with some neonates with low residual MTHFR activity. We attempted to rescue Mthfr−/− mice from postnatal death by betaine supplementation to their mothers throughout pregnancy and lactation. Betaine decreased the mortality of Mthfr−/− mice from 83% to 26% and significantly improved somatic development from postnatal day 1, compared with Mthfr−/− mice from unsupplemented dams. Biochemical evaluations demonstrated higher availability of betaine in suckling pups, decreased accumulation of homocysteine, and decreased flux through the trans-sulphuration pathway in liver and brain of Mthfr−/− pups from betaine-supplemented dams. We observed disturbances in proliferation and differentiation in the cerebellum and hippocampus in the knockout mice; these changes were ameliorated by betaine supplementation. The dramatic effects of betaine on survival and growth, and the partial reversibility of the biochemical and developmental anomalies in the brains of MTHFR-deficient mice, emphasize an important role for choline and betaine depletion in the pathogenesis of homocystinuria due to MTHFR deficiency.
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Abstract—A modest homocysteine elevation is associated with an increased cardiovascular risk. Marked circulating homocysteine elevations occur in homocystinuria due to cystathionine β-synthase (CβS) deficiency, a disorder associated with a greatly enhanced cardiovascular risk. Lowering homocysteine levels reduces this risk significantly. Because homocysteine-induced oxidative damage may contribute to vascular changes and extracellular superoxide dismutase (EC-SOD) is an important antioxidant in vascular tissue, we assessed EC-SOD and homocysteine in patients with homocystinuria. We measured circulating EC-SOD, total homocysteine (free plus bound), and methionine levels during the treatment of 21 patients with homocystinuria, 18 due to CβS deficiency, aged 8 to 59 years, and 3 with remethylating defects. We measured total homocysteine by immunoassay, EC-SOD by ELISA, and methionine by amino acid analysis and assessed interindividual and intraindividual relationships. There was a significant, positive relat...
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Homocystinuria is an inherited, inborn error of homocysteine metabolism, which leads to the abnormal accumulation of homocysteine and its metabolites in blood and urine, resulting in various complications. Variants in the cystathionine β-synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR) genes interrupt the formation of the corresponding enzymes and prevent homocysteine from being metabolised; hence, the homocysteine levels in plasma increase than the optimum levels.In the current study, eight clinically confirmed children with homocystinuria were detected to study the chosen variants in the CBS gene (c.833 T>C and c.19del) and in the MTHFR gene (c.665 C>T, c.1286 A>C) using SNaPshot mini-sequencing and direct sequencing.After screening eight patients, none had the c.833T>C, but four patients were in the homozygous state for the c.19del variant in the CBS gene. Furthermore, seven were heterozygous for c.1286A>C, while one patient was heterozygous for c.665C>T in the MTHFR gene.According to the results, c.19del is common in the studied cohort of Sri Lankan children, while c.833T>C is absent, whereas c.1286A>C was more frequent than c.665C>T. To our knowledge, the current study was the first report to discuss the genetic impact of homocystinuria in Sri Lanka; further comprehensive studies are necessary with a larger sample size to establish the association of these variants with the disease in Sri Lanka, which can be beneficial in enhanced patient care and for prospective studies.
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Homocystinuria is a medical condition that can have widespread and harmful effects on multiple organ systems within the body. This disease is caused by a deficiency in one of the enzymes involved in the methionine metabolism pathway. One example would be a deficiency in cystathionine-β-synthase (CBS), which is seen in classical homocystinuria. A deficiency in CBS can lead to elevated levels of homocysteine (HCY) and possible depletion of methionine and/or cysteine. There are several different treatment options for patients with this condition, one of which is the administration of the drug betaine. Here we review the use of betaine to decrease these elevated levels of homocysteine back to within normal ranges. Published literature indicates that the use of this choline derivative is most beneficial to patients who are either not compliant with the recommended low methionine and low protein diet or wish to consume a less restricted diet.
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Classical homocystinuria is a rare genetic disease caused by cystathionine β-synthase deficiency, resulting in homocysteine accumulation. Growing evidence suggests that reduced fat mass in patients with classical homocystinuria may be associated with alterations in choline and homocysteine pathways. This study aimed to evaluate the body composition of patients with classical homocystinuria, identifying changes in body fat percentage and correlating findings with biochemical markers of homocysteine and choline pathways, lipoprotein levels and bone mineral density (BMD) T-scores.Nine patients with classical homocystinuria were included in the study. Levels of homocysteine, methionine, cysteine, choline, betaine, dimethylglycine and ethanolamine were determined. Body composition was assessed by bioelectrical impedance analysis (BIA) in patients and in 18 controls. Data on the last BMD measurement and lipoprotein profile were obtained from medical records.Of 9 patients, 4 (44%) had a low body fat percentage, but no statistically significant differences were found between patients and controls. Homocysteine and methionine levels were negatively correlated with body mass index (BMI), while cysteine showed a positive correlation with BMI (p<0.05). There was a trend between total choline levels and body fat percentage (r=0.439, p=0.07). HDL cholesterol correlated with choline and ethanolamine levels (r=0.757, p=0.049; r=0.847, p=0.016, respectively), and total cholesterol also correlated with choline levels (r=0.775, p=0.041). There was no association between BMD T-scores and body composition.These results suggest that reduced fat mass is common in patients with classical homocystinuria, and that alterations in homocysteine and choline pathways affect body mass and lipid metabolism.
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MTHFR (methylenetetrahydrofolate reductase) catalyses the synthesis of 5-methyltetrahydrofolate, the folate derivative utilized in homocysteine remethylation to methionine. A severe deficiency of MTHFR results in hyperhomocysteinaemia and homocystinuria. Betaine supplementation has proven effective in ameliorating the biochemical abnormalities and the clinical course in patients with this deficiency. Mice with a complete knockout of MTHFR serve as a good animal model for homocystinuria; early postnatal death of these mice is common, as with some neonates with low residual MTHFR activity. We attempted to rescue Mthfr-/- mice from postnatal death by betaine supplementation to their mothers throughout pregnancy and lactation. Betaine decreased the mortality of Mthfr-/- mice from 83% to 26% and significantly improved somatic development from postnatal day 1, compared with Mthfr-/- mice from unsupplemented dams. Biochemical evaluations demonstrated higher availability of betaine in suckling pups, decreased accumulation of homocysteine, and decreased flux through the trans-sulphuration pathway in liver and brain of Mthfr-/- pups from betaine-supplemented dams. We observed disturbances in proliferation and differentiation in the cerebellum and hippocampus in the knockout mice; these changes were ameliorated by betaine supplementation. The dramatic effects of betaine on survival and growth, and the partial reversibility of the biochemical and developmental anomalies in the brains of MTHFR-deficient mice, emphasize an important role for choline and betaine depletion in the pathogenesis of homocystinuria due to MTHFR deficiency.
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Homocystinuria
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Homocystinuria is a rare inborn error of metabolism with the characteristic accumulation of homocysteine and its metabolites in the urine and blood. Homocystinuria is inherited in an autosomal recessive pattern where potential genetic impact for this condition is caused by genes associated with transsulfuration or methylation pathways, such as cystathionine-\(\beta\)-synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR), 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR), 5-methyltetrahydrofolate-homocysteine methyltransferase reductase (MTRR). In addition, deficiencies of cofactors (vitamins B2, B6, B12, and B9/folate) of the key enzymes in the main pathways are also causative factors of the disease. Clinical manifestations of the condition are dislocation of the eye lens, nearsightedness, skeletal abnormalities, and intellectual disabilities. The global prevalence of homocystinuria is approximately 1 in 200,000-335,000 worldwide, where more than 190 homocystinuria-associated CBS mutations, as well as 19 MTHFR gene mutations, have been documented worldwide, yet there are only a few researches have been done on Asian populations, and none in Sri Lanka. The current study focused on selected genetic variants in the CBS and MTHFR genes in a cohort of Sri Lankan children with homocystinuria, confirmed clinically and biochemically and followed up by a consultant chemical pathologist at Lady Ridgeway Hospital for Children, Colombo, Sri Lanka. Eight clinically confirmed patients were selected for the preliminary project within six months and screened for selected genetic variants in CBS and MTHFR genes. c.833 T>C and c.19del in CBS and c.665 C>T and c.1286 A>C in the MTHFR gene were selected and analyzed using SNaPshot mini-sequencing and direct sequencing. As per the analysis, no c.833T>C was reported, but four patients were in the homozygous state for the c.19del variant in the CBS gene. While seven were heterozygous for c.1286A>C, while one patient was heterozygous for c.665C>T in the MTHFR gene. In the study's conclusion, it was identified that c.19del is with a high prevalence in the studied cohort of Sri Lankan children, while c.833T>C is absent, whereas c.1286A>C was more frequent than c.665C>T. The current study was the first study to our knowledge discussing the genetic impact of homocystinuria in the Sri Lanka context; since it was a preliminary approach to establishing genetics variance of candidate genes in homocystinuria, further comprehensive studies would be suggested with a larger sample size with larger time frame as this is a rare disease though critical of seeking early detection for disease management.
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