Biomedical subjects
Publications and source records attributed to J M Trijbels.
Leigh syndrome is the phenotypical expression of a genetically heterogeneous cluster of disorders, with pyruvate dehydrogenase complex deficiency and respiratory chain disorders as the main biochemical causes. We report the first missense mutation within the nuclear encoded complex I subunit, NDUFS7, in 2 siblings with neuropathologically proven complex I-deficient Leigh syndrome.
The purpose of this study was the non-invasive quantitative determination by proton MR Spectroscopy (1H MRS) of alterations in cerebral metabolism in a 19-month-old male infant with severe global developmental delay caused by a Pyruvate Dehydrogenase Complex (PDHC) deficiency due to a mutation at the thiamine binding site. Two investigations were performed at different CSF thiamine concentrations to assess the effect of thiamine supplementation. 1H MR spectra were collected at different echo times (20-270 ms) from a voxel located in the striatum; spectroscopic imaging was done on a larger region including occipital white matter. The tissue levels of N-acetylaspartate and choline were in the normal range, while creatine appeared elevated. Abnormally high lactate and alanine signals were observed both in and outside the striatum; the levels of these metabolites were higher during the second measurement at a lower thiamine concentration. Abnormal cerebral levels of alanine have only been described once before in PDHC deficiency. The 1H MRS profile of this patient reflects the diversity of brain metabolite alterations in patients with this genetically heterogeneous disease.
NADH:ubiquinone oxidoreductase (complex I) is an extremely complicated multiprotein complex located in the inner mitochondrial membrane. Its main function is the transport of electrons from NADH to ubiquinone, which is accompanied by translocation of protons from the mitochondrial matrix to the intermembrane space. Human complex I appears to consist of 41 subunits of which 34 are encoded by nDNA. Here we report the cDNA sequences of the hitherto uncharacterized 8 nuclear encoded subunits, all located within the hydrophobic protein (HP) fraction of complex I. Now all currently known 41 proteins of human NADH:ubiquinone oxidoreductase have been characterized and reported in literature, which enables more complete mutational analysis studies of isolated complex I-deficient patients.
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Mitochondrial transmembrane carrier deficiencies are a recently discovered group of disorders, belonging to the so-called mitochondriocytopathies. We examined the human tissue distribution of carriers which are involved in the process of oxidative phosphorylation (adenine nucleotide translocator, phosphate carrier, and voltage-dependent anion channel) and some mitochondrial substrate carriers (2-oxoglutarate carrier, carnitine-acylcarnitine carrier, and citrate carrier). The tissue distribution on mRNA level of mitochondrial transport proteins appears to be roughly in correlation with the dependence of these tissues on mitochondrial energy production capacity. In general the main mRNA expression of carriers involved in mitochondrial energy metabolism occurs in skeletal muscle and heart. Expression in liver and pancreas differs between carriers. Expression in brain, placenta, lung, and kidney is lower than in the other tissues. Western and Northern blotting experiments show a comparable HVDAC1 protein and mRNA distribution for the tested tissues. Patient's studies showed that cultured skin fibroblasts may not be a reliable alternative for skeletal muscle in screening for human mitochondrial carrier defects.
Chronic renal failure (CRF) is associated, especially in young children, with delayed cognitive development of unknown origin. As cerebrospinal fluid (CSF) reflects the composition of the extracellular fluid of the brain, not only plasma but also CSF amino acids concentrations were determined in 8 infants (age 2-8 months) and 3 children (age 26, 32 and 56 months) with CRF (creatinine clearance 13 +/- 9 ml/min/ 1.73 m2). In three of these children investigations were repeated after six weeks of CAPD treatment. In the infants, a significant decrease was found in CSF of alpha-aminobutyric acid, valine, isoleucine, leucine, tyrosine, tryptophane, histidine and n-zeta-methyl-1-lysine, whereas there was a significant increase of 3-methylhistidine. In plasma serine, valine, leucine, tyrosine and histidine were significantly decreased, whereas there was a significant increase of aspartic acid, citrulline, and 3-methylhistidine. These abnormalities remained constant after the start of CAPD except for the normalization in CSF and plasma of 3-methylhistidine. These data indicate a generalized disturbance of amino acids in young children with CRF. An abnormal substrate is offered to the neurons and astroglia in children with CRF.
A male infant presented at 5 months of age with vomiting, developmental stagnation and convulsions. Complex I activity was in skeletal muscle 0.025 mU/mU CS (N 0.044-0.265) and in fibroblasts 0.046 mU/mU CS (N 0.100-0.307). Despite riboflavine supplementation progressive neurological deterioration occurred and he died at 14 months of age. During the mother's following pregnancy complex I activity was measured in chorionic villi and found mildly reduced, pregnancy was continued. A male infant was born who presented at 7 months of age with vomiting, developmental stagnation and hypotonia. Complex I activity was in skeletal muscle 0.031 mU/mU CS and in fibroblasts 0.100 mU/mU CS. There was progressive neurological deterioration and he died at 17 months of age. Complex I activity in autopsy liver of both patients was normal. Apparently, complex I deficiency presenting in infancy can have a fatal outcome despite only mild reduction of enzyme activity in skeletal muscle and/or fibroblasts, and chorionic villi and normal activity in liver.
The mitochondrial electron transport chain (mtETC) consists of four multi-subunit enzyme complexes. Complex I or NADH:ubiquinone oxidoreductase, the largest mtETC multisubunit complex, consists of approximately 41 subunits. Seven of these subunits are encoded by the mitochondrial genome, the remainder by the nuclear genome. Among the mitochondriocytopathies, complex I deficiencies are encountered frequently. Although some complex I deficiencies have been associated with mitochondrial DNA mutations, the genetic defect has not been elucidated in the majority of complex I-deficient patients. It is expected that many of these patients have mutations in the nuclear-encoded subunits of this complex, so vital for cellular energy production. After a brief summary of the current knowledge of complex I from cow, bacteria and fungi, this review presents the state of the art of the knowledge of the human nuclear-encoded complex I genes which, in the last 18 months, has made enormous progress. At present, the complete gene structure of four subunits and the cDNA structure of 18 of the 34 complex I nuclear-encoded subunits are known. Mapping of these subunits shows a random distribution over the chromosomes. The chromosomal localization is known for 14 complex I genes. Recently, the first mutation, a 5 bp duplication in the 18 kDa (AQDQ) subunit, has been reported. We expect that within 1 year all human nuclear-encoded complex I subunits will be cloned. Mutational analysis of these subunits is warranted in complex I-deficient patients and will not only be important for genetic counselling but will also extend the knowledge regarding the functional properties of the individual human complex I subunits.
UNLABELLED: An infant with severe deficiency of complex III combined with less severe deficiencies of complexes I, II and IV of the mitochondrial respiratory chain in skeletal muscle tissue presented with intra-uterine growth retardation, generalized hypotonia and delayed motor development. In the following 3.5 years muscle tone and motor development gradually normalized whereas the lactic acidosis and enzyme activities did not improve. CONCLUSION: This report documents a favourable clinical course in a child with combined respiratory chain deficiency despite persistent biochemical abnormalities.
Six children are presented with an isolated complex III deficiency in muscle tissue. More specifically, oxidation rates and ATP+CrP production rates from both pyruvate and succinate as substrates and/or the activity of decylubiquinol:cytochrome c oxidoreductase were all markedly reduced. Complex III deficiency was also present in liver of two patients tested, but could not be demonstrated in cultured fibroblasts of four patients tested. Mitochondrial DNA, extracted from muscle, was analyzed; no deletions or common point mutations were found. Four patients presented with a multi-organ disorder. Among these patients three presented at neonatal age with neurological signs and lactate elevation in blood and CSF, of whom two had severe neonatal Fanconi syndrome. One child, aged seven years, had encephalomyopathy, ophthalmoplegia, retinopathy and Wolff-Parkinson-White syndrome. The remaining two patients exhibited myopathy only, within the first year of life. Thus, like in other respiratory chain disorders, patients with complex III deficiency may present at any age and show variable symptoms and outcome, ranging from neonatal death to failure to thrive only. Apparently there are no clinical findings which are specific for complex III deficiency.
The first inborn error of creatine metabolism (guanidinoacetate methyltransferase [GAMT] deficiency) has recently been recognized in an infant with progressive extrapyramidal movement disorder. The diagnosis was established by creatine deficiency in the brain as detected by in vivo magnetic resonance spectroscopy and by defective GAMT activity and two mutant GAMT alleles in a liver biopsy. Here, we describe characteristic guanidino-compound patterns in body fluids of this index patient with GAMT deficiency. Concentrations of guanidino compounds (creatine and guanidinoacetate) and creatinine were determined by cation-exchange chromatography and by color reaction with picric acid, respectively, in urine, plasma, and cerebrospinal fluid (CSF). Creatine concentrations were low in plasma, CSF, and urine while guanidinoacetate concentrations were markedly elevated. Daily urinary creatinine excretion was low, whereas creatinine concentrations in random urine samples were not always discriminative. Guanidino compound to creatinine ratios were not informative, as low creatinine concentrations resulted in high values for all determined compounds. During a 22-month period of oral treatment with creatine-monohydrate, plasma and urinary creatine concentrations increased to levels high above the normal range, and daily urinary creatinine excretion-proportional to total body creatine-became normalized. Guanidinoacetate concentrations remained elevated even during additional substitution of ornithine, which inhibits guanidinoacetate synthesis in vitro. The results indicate that GAMT deficiency can be recognized noninvasively by determination of guanidino compounds (creatine and guanidinoacetate) in body fluids. A deficiency of creatine, but not an accumulation of guanidinoacetate, can be corrected by treatment with oral creatine substitution.
Elevated homocysteine (Hcy) levels are observed in two apparently unrelated diseases: neural-tube defects (NTD) and premature vascular disease. Defective human methionine synthase (MS) could result in elevated Hcy levels. We sequenced the coding region of MS in 8 hyperhomocysteinaemic patients (4 NTD patients and 4 patients with pregnancies complicated by spiral arterial disease, SAD). We identified only one mutation resulting in an amino acid substitution: an A-->G transition at bp 2756, converting an aspartic acid (D919) into a glycine (G). We screened genomic DNA for the presence of this mutation in 56 NTD patients, 69 mothers of children with NTD, 108 SAD patients and 364 controls. There was no increased prevalence of the GG and AG genotypes in NTD patients, their mothers or SAD patients. The D919G mutation does not seem to be a risk factor for NTD or vascular disease. We then examined the mean Hcy levels for each MS genotype. There was no correlation between GG- or AG-genotype and Hcy levels. The D919G mutation is thus a fairly prevalent, and probably benign polymorphism. This study, though limited, provides no evidence for a major involvement of MS in the aetiology of homocysteine-related diseases such as NTD or vascular disease.
OBJECTIVE: To assess the causes for delay in the diagnosis of homocystinuria. DESIGN: Clinical and laboratory data were collected from patients diagnosed as having homocystinuria due to cystathionine synthase deficiency, with special reference to the ages at which the patients had their first major signs of the disease, ectopia lentis was established, and homocystinuria was diagnosed. SETTING: University hospital in the Netherlands. SUBJECTS: 34 patients (18 males) in whom homocystinuria due to cystathionine synthase deficiency was diagnosed in the period 1970-94. RESULTS: Among 34 consecutively detected homocystinuria patients the mean age at diagnosis of homocystinuria was 24 (range 1-61) years. Despite frequent ocular manifestations, serious complications in the vascular, skeletal, and central nervous systems, and repeated examinations performed in these patients by clinicians of various disciplines, there was a mean delay of 11 (0-43) years between the first major signs of the disease (at mean age 13 (1-40) years) and the ultimate diagnosis of homocystinuria. Even when ectopia lentis was diagnosed (in 26 (76%) patients, mean age 18 (1-50) years), this did not lead to adequate biochemical analysis for homocystinuria at the time of detection, causing a mean diagnostic delay of 8 (0-24) years in these patients. CONCLUSIONS: Three factors should have precipitated the diagnosis of homocystinuria: early recognition that unusual myopia (high, very high, abnormal progressive, or at young age) was caused by subluxation of the ocular lenses; awareness that the occurrence of myopia combined with systemic complications ("myopia plus") might be due to homocystinuria; and appropriate biochemical investigations carried out in patients with ectopia lentis and in their siblings.
6-mercaptopurine (6MP) cytotoxicity is caused by thioguanine and methylthioinosine nucleotides. Thiopurine methylation occurs to a large extent in vivo and in vitro. In this reaction, S-adenosyl-L-methionine (AdoMet), produced from methionine and ATP, is converted into S-adenosyl-L-homocysteine (AdoHcy) which, in turn, is hydrolyzed into homocysteine. Remethylation of homocysteine into methionine is inhibited by methotrexate (MTX). In cultured lymphoblasts, AdoMet: AdoHcy ratio and DNA methylation decrease after incubation with 6MP. The aim of the present study was to investigate the influence of high-dose 6MP on the methylation capacity in children with acute lymphoblastic leukemia. Five patients received 4 courses with high-dose intravenous MTX (5' g.m-2 in 24 hr) immediately followed by high-dose 6MP (1300 mg.m-2 in 24 hr). Five control patients received high-dose MTX and oral 6MP (25 mg.m -2 daily for 8 weeks). Leucovorin rescue was started at 36 hr in both groups. In the intravenous 6MP group, 6-methylmercaptopurine, its riboside, and 6-methylmercapto-8-hydroxypurine were detectable in plasma in concentrations of 0.3-2.6 muM (6MP steady state levels: 11.6 muM). In red blood cells, mean methylthioinosine nucleotide levels were one third of those of ATP (13.1 nmol/10(8)). AdoHcy levels (10 pmol/10(8)) remained constant in both groups and AdoMet was not detectable ( < 20 pmol/10(8)). In both groups, plasma homocysteine increased and methionine decreased following administration of MTX. The delay in the recovery of methionine in the intravenous 6MP group after MTX infusion is probably the result of an increased demand on methyl groups during 6MP infusion.
Thiopurine methyltransferase (TPMT) is an important enzyme in the metabolism of 6-mercaptopurine (6MP), which is used in the treatment of acute lymphoblastic leukemia (ALL). TPMT catalyzes the formation of methylthioinosine monophosphate (MetIMP), which is cytotoxic for cultured cell lines, and it plays a role in detoxification of 6MP. Population studies show a genetic polymorphism for TPMT with both high and low activity alleles. About 1 of 300 subjects is homozygous for the low activity. The function TPMT plays in detoxification or therapeutic efficacy of 6MP in vivo is not clear. In this article the genetic polymorphism of TPMT is reviewed and the contribution of TPMT to the cytotoxic action, or detoxification, of 6MP in children with ALL is discussed. Induction of TPMT activity has been described during the treatment for ALL. We performed a pilot study on the influence of high-dose 6MP infusions (1300 mg/m2 in 24 h) on TPMT activity of peripheral blood mononuclear cells (pMNC) of eleven patients with ALL. The TPMT activities were in, or, above the normal range. There was no statistically significant difference between the TPMT activities before and after the 6MP infusions. MetIMP levels in pMNC increased during successive courses. This might be explained by TPMT induction, but other explanations are plausible as well. Twenty five percent of the TPMT assays failed, because less than the necessary 5.10(6) pMNC could be isolated from the blood of leukopenic patients. Red blood cells can not be used for TPMT measurements, since transfusions are frequently required during the treatment with 6MP infusions. Therefore, the influence of high-dose 6MP infusions on TPMT activity can only be investigated further when a TPMT assay which requires less pMNC has been developed.
Point mutations in mitochondrial DNA, as found in MELAS, MERRF, NARP and other syndromes, are inherited via the maternal lineage. Genetic counselling can be beneficial, but prenatal diagnosis is not advantageous in these syndromes. Empirical data about the recurrence risk can be applied in Leber disease (LHON). Mitochondrial disorders not associated with a point mutation have a sporadic nature (large deletions/duplications in mitochondrial DNA) or are transmitted according to Mendelian laws. Autosomal dominant inheritance is likely to be found in disorders with depletion of mitochondrial DNA. X-linked mode of inheritance is seen in Menkes disease, Barth syndrome, and in deficiencies of the E1 alpha subunit of the pyruvate dehydrogenase complex. Mutation analysis or linkage studies can be applied for carrier detection and prenatal diagnosis in these three types of mitochondriopathies. The majority of the disorders with a disturbed mitochondrial energy metabolism are likely inherited in an autosomal recessive mode. Prenatal diagnosis can be performed in the cases of cytochrome c oxidase and NADH dehydrogenase deficiencies in chorionic villi in selected families.
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PURPOSE: We investigated the metabolism of high dose 6 mercaptopurine (HD-6MP) infusions and its influence on the metabolism by allopurinol, an inhibitor of xanthine oxidase, the enzyme that catabolizes 6MP into thioxanthine and thiouric acid. PATIENTS AND METHODS: Nine patients (aged 2-11 years) with non-Hodgkin lymphoma (NHL) were treated with HD-6MP (1300 mg/m(2).24h) within a therapeutic window after diagnosis. Four patients received oral allopurinol (200 mg/m(2).day) to prevent urate nephropathy, and five did not. Plasma and RBC were isolated before and 4, 20, 24, 28, and 48h after the start of the infusion. All measurements were performed with HPLC. RESULTS: Considerable variations were found in the plasma levels of 6MP, thioxanthine, and thiouric acid and of RBC-MeTIN levels. 6MP-riboside was not detectable, and MeMP and MeMPR levels were <1.3 muM in the plasma. In general, 6MP, thioxanthine, and MeMP levels in plasma were higher, and thiouric acid plasma levels and RBC-MeTIN levels were lower in the patients treated with allopurinol compared to those who did not receive allopurinol. CONCLUSIONS: 6MP is extensively metabolized in patients with NHL treated with HD-6MP. Thiopurine methylation, at the levels of nucleotide, nucleoside, and base, is an important metabolic pathway after HD-6MP. Co-administration of allopurinol can result in both a decreased catabolism and anabolism of 6MP compared to treatment with HD-6MP alone. This observation may have consequences for the therapeutic efficacy and toxic effects of 6MP in combination with allopurinol.