5-methyltetrahydrofolate and Metabolism--Inborn-Errors

Analysis of pyridoxal 5'-phosphate (PLP) concentration in 256 cerebrospinal fluid (CSF) samples from patients with neurological symptoms showed that the variance is greater than indicated by previous studies. The age-related lower reference limit has been revised to detect inborn errors of metabolism that lead to PLP depletion without a high false positive rate: < 30 days, 26 nmol/L; 30 days to 12 months, 14 nmol/L; 1-2 years, 11 nmol/L; > 3 years, 10 nmol/L. Inborn errors leading to PLP concentrations below these values include pyridoxine-dependent epilepsy due to antiquitin deficiency, and molybdenum cofactor deficiency that leads to the accumulation of sulfite, a nucleophile capable of reacting with PLP. Low PLP levels were also seen in a group of children with transiently elevated urinary excretion of sulfite and/or sulfocysteine, suggesting that there may be other situations in which sulfite accumulates and inactivates PLP. There was no evidence that seizures or the anticonvulsant drugs prescribed for patients in this study led to significant lowering of CSF PLP. A small proportion of patients receiving L-dopa therapy were found to have a CSF PLP concentration below the appropriate reference range. This may have implications for monitoring and treatment. A positive correlation was seen between the CSF PLP and 5-methyl-tetrahydrofolate (5-MTHF) and tetrahydrobiopterin (BH(4)) concentrations. All are susceptible to attack by nucleophiles and oxygen-derived free-radicals, and CSF has relatively low concentrations of other molecules that can react with these compounds. Further studies of CSF PLP levels in a wide range of neurological diseases might lead to improved understanding of pathogenesis and possibilities for treatment.

Topics: Adolescent; Adult; Biopterins; Child; Child, Preschool; Cysteine; Epilepsy; False Positive Reactions; Female; Free Radicals; Humans; Infant; Infant, Newborn; Levodopa; Male; Metabolism, Inborn Errors; Middle Aged; Nervous System Diseases; Oxygen; Pyridoxal Phosphate; Reference Values; Reproducibility of Results; Sulfites; Tetrahydrofolates

1. Folate deficiency, or inborn errors of folate metabolism, cause reduced turnover of 5-hydroxytryptamine (serotonin), and perhaps dopamine, in the central nervous system. The mechanism by which this occurs are not known. One possibility is that this is mediated by deficiency of the methyl-donor S-adenosylmethionine. 2. To test this in humans, we have measured cerebrospinal fluid concentrations of 5-hydroxyindoleacetic acid and homovanillic acid, metabolites of 5-hydroxytryptamine and dopamine, respectively, in children with inborn errors of the methyl-transfer pathway. These children are naturally deficient in 5-methyltetrahydrofolate, S-adenosylmethionine or both before treatment, and replete with S-adenosylmethionine, but not necessarily with 5-methyltetrahydrofolate, during treatment. 3. Children with subnormal cerebrospinal fluid concentrations of 5-methyltetrahydrofolate had significantly reduced concentrations of 5-hydroxyindoleacetic acid and homovanillic acid. Children with subnormal cerebrospinal fluid concentrations of S-adenosylmethionine did not have significantly reduced concentrations of these metabolites. 4. We conclude that the mechanism by which deficiency of 5-methyltetrahydrofolate causes reduced 5-hydroxytryptamine and dopamine turnover is unlikely to be mediated by S-adenosylmethionine.

Topics: Adult; Child; Child, Preschool; Dopamine; Homovanillic Acid; Humans; Hydroxyindoleacetic Acid; Infant; Metabolism, Inborn Errors; S-Adenosylmethionine; Serotonin; Tetrahydrofolates

Human skin fibroblasts derived from patients with all seven known inborn errors of vitamin B12 metabolism have been studied for functional integrity of methylmalonyl CoA mutase and methionine synthase. Cocultivation of cblC and cblF fibroblasts in the absence of polyethylene glycol resulted in a twofold increase over the expected in both [14C]propionate and [14C]methyltetrahydrofolate incorporation into acid-precipitable material, suggesting that metabolic cooperation between cells occurs. This correction in phenotype seems to be mutant class selective since cblD fibroblasts, which are biochemically similar to cblC cells, do not cooperate metabolically when mixed with cblF cells. These observations lend further support to the division of cblC and cblD diseases into discrete classes.

Topics: 5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; Cell Division; Cells, Cultured; Fibroblasts; Humans; Kinetics; Metabolism, Inborn Errors; Methylmalonyl-CoA Mutase; Propionates; Tetrahydrofolates; Vitamin B 12

Topics: Amino Acid Metabolism, Inborn Errors; Biological Transport; Cell Membrane; Cells, Cultured; Diffusion; Electrochemistry; Fibroblasts; Folic Acid; Humans; Lysine; Membrane Potentials; Metabolism, Inborn Errors; Mutation; Potassium; Tetrahydrofolates

We studied two brothers (J.R. and M.R.) with the cobalamin D variant of congenital methylmalonic aciduria-homocystinuria, whose previously reported lack of megaloblastic anemia conflicted with current concepts of cobalamin's role in DNA synthesis and the "methyltetrahydrofolate (MTHF) trap" hypothesis. Both subjects were indeed hematologically normal, although J.R. had a mean corpuscular volume of 96 fl. However, both demonstrated abnormalities in the deoxyuridine suppression test. J.R. had an abnormal suppression value of 21.0% (normal less than 10%) that was correctable by adding hydroxocobalamin or folic acid in vitro but not MTHF. M.R. had normal suppression (8.9%), but demonstrated worsening (18.6%) when MTHF was added. J.R.'s classical deoxyuridine suppression pattern of cobalamin deficiency thus supports the trap hypothesis. However, his lack of comparable morphological changes suggests that impaired de novo thymidylate synthesis and the trap hypothesis, though valid, may not fully account for the megaloblastic maturation accompanying cobalamin deficiency. Equally noteworthy was the deleterious effect of MTHF on M.R.'s marrow, suggesting its potential usefulness as an in vitro "stress test" for latent cobalamin abnormality.

Topics: Adolescent; Adult; Anemia, Megaloblastic; Bone Marrow; Deoxyuridine; Homocystinuria; Humans; Male; Metabolism, Inborn Errors; Methylmalonic Acid; Tetrahydrofolates; Thymidine; Vitamin B 12