A biallelic pathogenic variant in the OGDH gene results in a neurological disorder with features of a mitochondrial disease

2-Oxoglutarate dehydrogenase (OGDH) is a rate-limiting enzyme in the mitochondrial TCA cycle, encoded by the OGDH gene. α-Ketoglutarate dehydrogenase (OGDH) deficiency was previously reported in association with developmental delay, hypotonia, and movement disorders and metabolic decompensation, with no genetic data provided. Using whole exome sequencing, we identified two individuals carrying a homozygous missense variant c.959A>G (p.N320S) in the OGDH gene. These individuals presented with global developmental delay, elevated lactate, ataxia and seizure. Fibroblast analysis and modeling of the mutation in Drosophila were used to evaluate pathogenicity of the variant. Skin fibroblasts from subject # 2 showed a decrease in both OGDH protein and enzyme activity. Transfection of human OGDH cDNA in HEK293 cells carrying p.N320S also produced significantly lower protein levels compared to those with wild-type cDNA. Loss of Drosophila Ogdh (dOgdh) caused early developmental lethality, rescued by expressing wild-type dOgdh (dOgdh^WT ) or human OGDH (OGDH^WT ) cDNA. In contrast, expression to the mutant OGDH (OGDH^N320S ) or dOgdh carrying homologous mutations to human OGDH p.N320S variant (dOgdh^N324S ) failed to rescue lethality of dOgdh null mutants. Knockdown of dOgdh in the nervous system resulted in locomotion defects which were rescued by dOgdh^WT expression but not by dOgdh^N324S expression. Collectively, the results indicate that c.959A>G variant in OGDH leads to an amino acid change (p.N320S) causing a severe loss of OGDH protein function. Our study establishes in the first time a genetic link between an OGDH gene mutation and OGDH deficiency.

Multi-Target Analysis and Design of Mitochondrial Metabolism

Analyzing and optimizing biological models is often identified as a research priority in biomedical engineering. An important feature of a model should be the ability to find the best condition in which an organism has to be grown in order to reach specific optimal output values chosen by the researcher. In this work, we take into account a mitochondrial model analyzed with flux-balance analysis. The optimal design and assessment of these models is achieved through single- and/or multi-objective optimization techniques driven by epsilon-dominance and identifiability analysis. Our optimization algorithm searches for the values of the flux rates that optimize multiple cellular functions simultaneously. The optimization of the fluxes of the metabolic network includes not only input fluxes, but also internal fluxes. A faster convergence process with robust candidate solutions is permitted by a relaxed Pareto dominance, regulating the granularity of the approximation of the desired Pareto front. We find that the maximum ATP production is linked to a total consumption of NADH, and reaching the maximum amount of NADH leads to an increasing request of NADH from the external environment. Furthermore, the identifiability analysis characterizes the type and the stage of three monogenic diseases. Finally, we propose a new methodology to extend any constraint-based model using protein abundances.

Rare case with megaloblastic anaemia

A nine years old boy presented with history of pallor and anaemia since early infancy along with neural hearing loss responding to empirical multivitamin and folic acid therapy started on basis of blood complete picture showing anaemia and megaloblastic anaemia. On investigation he was diagnosed with Thiamine Responsive Megaloblastic Anaemia, a very rare condition in our settings.

Identification of a SLC19A2 nonsense mutation in Persian families with thiamine-responsive megaloblastic anemia

Thiamine-responsive megaloblastic anemia (TRMA) is an autosomal recessive syndrome characterized by early-onset anemia, diabetes, and hearing loss caused by mutations in the SLC19A2 gene. We studied the genetic cause and clinical features of this condition in patients from the Persian population. A clinical and molecular investigation was performed in four patients from three families and their healthy family members. All had the typical diagnostic criteria. The onset of hearing loss in three patients was at birth and one patient also had a stroke and seizure disorder. Thiamine treatment effectively corrected the anemia in all of our patients but did not prevent hearing loss. Diabetes was improved in one patient who presented at the age of 8months with anemia and diabetes after 2months of starting thiamine. The coding regions of SLC19A2 were sequenced in all patients. The identified mutation was tested in all members of the families. Molecular analyses identified a homozygous nonsense mutation c.697C>T (p.Gln233*) as the cause of the disease in all families. This mutation was previously reported in a Turkish patient with TRMA and is likely to be a founder mutation in the Persian population.

Deficits in the mitochondrial enzyme α-ketoglutarate dehydrogenase lead to Alzheimer's disease-like calcium dysregulation

Understanding the molecular sequence of events that culminate in multiple abnormalities in brains from patients that died with Alzheimer's disease (AD) will help to reveal the mechanisms of the disease and identify upstream events as therapeutic targets. The activity of the mitochondrial α-ketoglutarate dehydrogenase complex (KGDHC) in homogenates from autopsy brain declines with AD. Experimental reductions in KGDHC in mouse models of AD promote plaque and tangle formation, the hallmark pathologies of AD. We hypothesize that deficits in KGDHC also lead to the abnormalities in endoplasmic reticulum (ER) calcium stores and cytosolic calcium following K(+) depolarization that occurs in cells from AD patients and transgenic models of AD. The activity of the mitochondrial enzyme KGDHC was diminished acutely (minutes), long-term (days), or chronically (weeks). Acute inhibition of KGDHC produced effects on calcium opposite to those in AD, while the chronic or long-term inhibition of KGDHC mimicked the AD-related changes in calcium. Divergent changes in proteins released from the mitochondria that affect endoplasmic reticulum calcium channels may underlie the selective cellular consequences of acute versus longer term inhibition of KGDHC. The results suggest that the mitochondrial abnormalities in AD can be upstream of those in calcium.

Thiamine-responsive megaloblastic anemia syndrome: a novel mutation

The thiamine-responsive megaloblastic anemia syndrome (TRMA) is an autosomal recessive disorder characterized by diabetes mellitus, megaloblastic anemia and sensorineural hearing loss due to mutations in SLC 19A2 that encodes a thiamine transporter protein. The disease can manifest at any time between infancy and adolescence, and not all cardinal findings are present initially. The anemia typically improves significantly with pharmacological doses of thiamine. Variable improvement in diabetes is also noted. However, the hearing loss is apparently irreversible, although a delay in the onset of deafness may be possible. We present a 2-year old girl with non-autoimmune diabetes mellitus and anemia in whom we found a novelc.95T>A (leu32X) mutation in the SLC19A2 gene in this study.Our patient with this new mutation did not suffer from hearing loss.

[Ultrastructure of coronary microvessels in conditions of heart reperfusion following prolonged ischemia while applying various methods of artificial hypothermia]

It has been found out that in children with Roger's disease corrected in the conditions of two fundamentally different procedures of anesthetic management, myocardial reperfusion after cardiac arrest under artificial hypothermic circulation is accompanied by obstruction of more than 30% of coronary bed microvessels with hydropic endothelial cells or their cystiform fragments. The content of necrotic cells increases, while the "working" cells demonstrate a decrease in myocropinocytotic transport characteristics. Circulatory arrest under perfusionless hypothermia and immersion reperfusion do not result in a dramatic change of general morphology of microvessels as compared to the control group, while a heterogenic response of the structures responsible for transendothelial transfer of macromolecules provides the basis for recovery of the endothelium structure and function, as a patient's temperature reaches a standard value.

Altered metabolic flux due to deletion of odhA causes L-glutamate overproduction in Corynebacterium glutamicum

L-glutamate overproduction in Corynebacterium glutamicum, a biotin auxotroph, is induced by biotin limitation or by treatment with certain fatty acid ester surfactants or with penicillin. We have analyzed the relationship between the inductions, 2-oxoglutarate dehydrogenase complex (ODHC) activity, and L-glutamate production. Here we show that a strain deleted for odhA and completely lacking ODHC activity produces L-glutamate as efficiently as the induced wild type (27.8 mmol/g [dry weight] of cells for the ohdA deletion strain compared with only 1.0 mmol/g [dry weight] of cells for the uninduced wild type). This level of production is achieved without any induction or alteration in the fatty acid composition of the cells, showing that L-glutamate overproduction can be caused by the change in metabolic flux alone. Interestingly, the L-glutamate productivity of the odhA-deleted strain is increased about 10% by each of the L-glutamate-producing inductions, showing that the change in metabolic flux resulting from the odhA deletion and the inductions have additive effects on L-glutamate overproduction. Tween 40 was indicated to induce drastic metabolic change leading to L-glutamate overproduction in the odhA-deleted strain. Furthermore, optimizing the metabolic flux from 2-oxoglutarate to L-glutamate by tuning glutamate dehydrogenase activity increased the l-glutamate production of the odhA-deleted strain.

A novel mutation in the dihydrolipoamide dehydrogenase E3 subunit gene (DLD) resulting in an atypical form of α-ketoglutarate dehydrogenase deficiency

The alpha-ketoglutarate dehydrogenase complex (KGDC) catalyses the decarboxylation of alpha-ketoglutarate into succinyl-coenzyme A in the Krebs cycle. This enzymatic complex is made up of three subunits (E1, encoded by PDHA1; E2, encoded by DLST; and E3, encoded by DLD). The E3 subunit is common to two other enzymatic complexes, namely pyruvate dehydrogenase complex (PDC) and branched-chain ketoacid dehydrogenase complex (BCKDC). KGDC deficiency is a rare autosomal recessive disorder, most often presenting with severe encephalopathy and hyperlactatemia with neonatal onset. We found a KGDC deficiency in cultured skin fibroblasts from three siblings born to consanguinous parents. E3 subunit activity was shown to be deficient (20% of control values), despite the absence of usual clinical clues to E3 deficiency, i.e. accumulation of pyruvate and branched-chain amino acids in plasma and branched-chain alpha-ketoacids in urine. RT-PCR of E3 mRNA from the three patients, followed by sequencing, revealed an homozygous c.1444A>G substitution located in E3 exon 13, predictive of a p.R482G (or R447G in the processed gene product) substitution in a highly conserved domain of the protein. Only eleven E3 mutations have been reported so far. The only other case of E3 deficiency without clinical or biochemical evidences of PDC and BCKDC deficiencies has been ascribed to a c.1436A>T (p.D479V; or D444V in the processed gene product) mutation, very close to the mutation reported herein. Since c.1444A>G (p.R482G; or R447G in the processed gene product) and c.1436A>T (p.D479V; or D444V in the processed gene product) lie within the interface domain of E3 with E2 (KGDC and BCKDC) or the E3-binding protein (PDC), our data suggest that interaction of E3 with these other subunits differs in some extent among KGDC, PDC, and BCKDC.

Aerobic growth deficient Haemophilus influenzae mutants are non-virulent: implications on metabolism

We investigated aerobic metabolism in Haemophilus influenzae to better understand its essential physiological growth pathways. We describe the isolation and characterization of transposon insertions leading to knockout mutations in lpdA, encoding dihydrolipoamide dehydrogenase. H. influenzae Rd lpdA::Tn10d-cat mutants were unable to grow aerobically and an H. influenzae type b lpdA::Tn10d-cat mutant was significantly attenuated in an infant rat infection model. Since LpdA is a functional subunit of both pyruvate dehydrogenase (aceEF) and alpha-ketoglutarate dehydrogenase (sucAB) the phenotype of the lpdA mutant was further explored by creating separate knockout mutants in the sucAB and aceEF loci. DeltaaceEF and deltasucAB mutants were both significantly attenuated in virulence in the infant rat, but only the sucAB mutant was able to grow aerobically. We therefore conclude that the ability for aerobic growth is critical for invasive disease, and furthermore that a TCA cycle enzyme, alpha-ketoglutarate dehydrogenase, appears to contribute a key metabolic function in vivo, but is not required for growth under laboratory conditions.

Procyclic Trypanosoma brucei do not use Krebs cycle activity for energy generation

The importance of a functional Krebs cycle for energy generation in the procyclic stage of Trypanosoma brucei was investigated under physiological conditions during logarithmic phase growth of a pleomorphic parasite strain. Wild type procyclic cells and mutants with targeted deletion of the gene coding for aconitase were derived by synchronous in vitro differentiation from wild type and mutant (Delta aco::NEO/Delta aco::HYG) bloodstream stage parasites, respectively, where aconitase is not expressed and is dispensable. No differences in intracellular levels of glycolytic and Krebs cycle intermediates were found in procyclic wild type and mutant cells, except for citrate that accumulated up to 90-fold in the mutants, confirming the absence of aconitase activity. Surprisingly, deletion of aconitase did not change differentiation nor the growth rate or the intracellular ATP/ADP ratio in those cells. Metabolic studies using radioactively labeled substrates and NMR analysis demonstrated that glucose and proline were not degraded via the Krebs cycle to CO(2). Instead, glucose was degraded to acetate, succinate, and alanine, whereas proline was degraded to succinate. Importantly, there was absolutely no difference in the metabolic products released by wild type and aconitase knockout parasites, and both were for survival strictly dependent on respiration via the mitochondrial electron transport chain. Hence, although the Krebs cycle enzymes are present, procyclic T. brucei do not use Krebs cycle activity for energy generation, but the mitochondrial respiratory chain is essential for survival and growth. We therefore propose a revised model of the energy metabolism of procyclic T. brucei.

DOOR syndrome: deficiency of E1 component of the 2-oxoglutarate dehydrogenase complex

Four patients from three families with the clinical features of DOOR syndrome (onycho-osteodystrophy, dystrophic thumbs, sensorineural deafness, and increased urinary levels of 2-oxoglutarate) are the subjects of this report. Our report deals with the autosomal recessive form of the disease, wherein the activity of 2-oxoglutarate decarboxylase (E1(0)) in fibroblasts and white blood cells of the patients is decreased. The activity of E1(0) in all patients' fibroblasts and white blood cells was significantly lower compared to the controls. This study demonstrates for the first time that E1(0) deficiency is an important biochemical marker for the autosomal recessive form of DOOR syndrome.

The alpha-ketoglutarate dehydrogenase complex

The alpha-ketoglutarate dehydrogenase complex (KGDHC) is an important mitochondrial constituent, and deficiency of KGDHC is associated with a number of neurological disorders. KGDHC is composed of three proteins, each encoded on a different and well-characterized gene. The sequences of the human proteins are known. The organization of the proteins into a large, ordered multienzyme complex (a "metabolon") has been well studied in prokaryotic and eukaryotic species. KGDHC catalyzes a critical step in the Krebs tricarboxylic acid cycle, which is also a step in the metabolism of the potentially excitotoxic neurotransmitter glutamate. A number of metabolites modify the activity of KGDHC, including inactivation by 4-hydroxynonenal and other reactive oxygen species (ROS). In human brain, the activity of KGDHC is lower than that of any other enzyme of energy metabolism, including phosphofructokinase, aconitase, and the electron transport complexes. Deficiencies of KGDHC are likely to impair brain energy metabolism and therefore brain function, and lead to manifestations of brain disease. In general, the clinical manifestations of KGDHC deficiency relate to the severity of the deficiency. Several such disorders have been recognized: infantile lactic acidosis, psychomotor retardation in childhood, intermittent neuropsychiatric disease with ataxia and other motor manifestations, Friedreich's and other spinocerebellar ataxias, Parkinson's disease, and Alzheimer's disease (AD). A KGDHC gene has been associated with the first two and last two of these disorders. KGDHC is not uniformly distributed in human brain, and the neurons that appear selectively vulnerable in human temporal cortex in AD are enriched in KGDHC. We hypothesize that variations in KGDHC that are not deleterious during reproductive life become deleterious with aging, perhaps by predisposing this mitochondrial metabolon to oxidative damage.

2-ketoglutarate dehydrogenase deficiency with intermittent 2-ketoglutaric aciduria

2-ketoglutarate dehydrogenase (KGD) deficiency is a rare disorder of the tricarboxylic acid cycle. To date, 7 patients have been reported with clinical symptoms suggesting a neurodegenerative disease. We report a new patient in whom urinary excretion of 2-ketoglutaric acid (KGA) was intermittently found to be within normal ranges. At birth, the male patient suffered from mild perinatal asphyxia due to meconium aspiration. During the first months of life, he developed an opisthotonus, hyperexcitability and truncal hypertonia. At the present age of 14 months, these neurological symptoms became less pronounced. A cranial MRI was normal. Urinary 2-KGA excretion was found to be intermittently increased in 3 of 6 analyses between 2 weeks and 14 months of age (5-1700 mmol/mol creatinine, controls: < 340 mmol/mol creatinine). 2-KGA was not increased in plasma and CSF. Diagnosis was confirmed by measurement of decreased 2-KGD activity in cultured skin fibroblasts. This report demonstrates that the diagnosis of 2-KGD deficiency can easily be missed. In case of doubt, 2-KGD activity should be measured in fibroblasts. The clinical and long-term outcome of patients with 2-KGD deficiency is unknown. Further reports and long-term evaluation are required.

Lipoamide dehydrogenase deficiency due to a novel mutation in the interface domain

An infant with a neurodegenerative disorder accompanied by lactic acidemia is described. In muscle homogenate, the activity of lipoamide dehydrogenase (LAD), the third catalytic subunit of pyruvate dehydrogenase complex (PDHc), alpha-ketoglutarate dehydrogenase complex (KGDHc), and branched-chain keto acid dehydrogenase complex was reduced to 15% of the control. The activity of PDHc was undetectable and the activity of KGDHc was 2% of the control mean. The immunoreactive LAD protein was reduced to about 10% of the control. Direct sequencing of LAD cDNA revealed only one mutation, substituting Asp for Val at position 479 of the precursor form. The mutation resides within the interface domain and likely perturbs stable dimerization. The phenotypic heterogeneity in LAD deficiency is not directly correlated with the residual LAD activity but rather with its impact on the multienzymatic complex activity.

Immunochemical characterization of the deficiency of the alpha-ketoglutarate dehydrogenase complex in thiamine-deficient rat brain

Mitochondrial dysfunction is a common feature of many neurodegenerative disorders. The metabolic encephalopathy caused by thiamine deficiency (TD) is a classic example in which an impairment of cerebral oxidative metabolism leads to selective cell death. In experimental TD in rodents, a reduction in the activity of the thiamine diphosphate-dependent, mitochondrial enzyme alpha-ketoglutarate dehydrogenase complex (KGDHC) occurs before the onset of pathologic lesions and is among the earliest biochemical deficits found. To understand the molecular basis and the significance of the deficiency of KGDHC in TD-induced brain damage, the enzyme activity and protein levels of KGDHC were analyzed. The effect of TD on the subregional/cellular distribution of KGDHC and the anatomic relation of KGDHC with selective cell death were also tested by immunocytochemistry. Consistent with several previous studies, TD dramatically reduced KGDHC activity in both anatomically damaged (thalamus and inferior colliculus) and spared (cerebral cortex) regions. Immunocytochemistry revealed no apparent correlation of regional KGDHC immunoreactivity or its response to TD with affected regions in TD. The basis of the enzymatic and immunocytochemical behavior of KGDHC was further assessed by quantitative immunoblots, using antibodies specific for each of the three KGDHC components. Despite the marked decrease of KGDHC activity in TD, no reduction of any of the three KGDHC protein levels was found. Thus, TD impairs the efficacy of the KGDHC catalytic machinery, whereas the concentration of protein molecules persists. The generalized decline of KGDHC activity with no apparent anatomic selectivity is consistent with the notion that the compromised mitochondrial oxidation sensitizes the brain cells to various other insults that precipitate the cell death. The current TD model provides a relevant experimental system to understand the molecular basis of many neurodegenerative conditions in which mitochondrial dysfunction and KGDHC deficiency are prominent features.

Inborn errors of the Krebs cycle: a group of unusual mitochondrial diseases in human

Krebs cycle disorders constitute a group of rare human diseases which present an amazing complexity considering our current knowledge on the Krebs cycle function and biogenesis. Acting as a turntable of cell metabolism, it is ubiquitously distributed in the organism and its enzyme components encoded by supposedly typical house-keeping genes. However, the investigation of patients presenting specific defects of Krebs cycle enzymes, resulting from deleterious mutations of the considered genes, leads to reconsider this simple envision by revealing organ-specific impairments, mostly affecting neuromuscular system. This often leaves aside organs the metabolism of which strongly depends on mitochondrial energy metabolism as well, such as heart, kidney or liver. Additionally, in some patients, a complex pattern of tissue-specific enzyme defect was also observed. The lack of functional additional copies of Krebs cycle genes suggests that the complex expression pattern should be ascribed to tissue-specific regulations of transcriptional and/or translational activities, together with a variable cell adaptability to Krebs cycle functional defects.

Hypothesis on cellular ATP depletion and adenosine release as causes of heart failure and vasodilatation in cardiovascular beriberi

Cardiovascular beriberi is a syndrome caused by thiamine deficiency and characterized by systemic vasodilatation, heart failure and lactic acidosis. The occurrence of heart failure and vasodilatation is yet unexplained: neither theoretical nor experimental data are known. In this article, it is suggested that a fall of cellular ATP levels causes heart failure and that the release of adenosine is the cause of vasodilatation.

Cerebellar alpha-ketoglutarate dehydrogenase activity is reduced in spinocerebellar ataxia type 1

We measured the activity of the thiamine pyrophosphate-dependent enzyme alpha-ketoglutarate dehydrogenase complex in postmortem brain of 12 patients with the spinocerebellar ataxia type 1 form of olivopontocerebellar atrophy. alpha-Ketoglutarate dehydrogenase complex activity measured in the absence of thiamine pyrophosphate was markedly reduced (-72%) in olivopontocerebellar atrophy cerebellar cortex. Decreased activity of this key rate-limiting Krebs cycle enzyme could compromise cerebellar energy metabolism and excitatory amino acid synthesis and thereby contribute to the brain dysfunction of olivopontocerebellar atrophy.

Abnormality of the alpha-ketoglutarate dehydrogenase complex in fibroblasts from familial Alzheimer's disease

To test whether previously demonstrated reductions in the activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC) in Alzheimer's disease (AD) brain also occur in morphologically normal AD tissues, we examined KGDHC in cultured skin fibroblasts from patients with familial AD (FAD). KGDHC activity was reduced by 44% in the FAD cells (p < 0.002) from the 4 families studied, including a within-kindred comparison of affected and escapee subjects in the chromosome 14q24.3-linked Nova Scotia kindred. The activities of several other glutamate- and glutamine-metabolizing enzymes were normal in the FAD cells, as was the activity of another mitochondrial multienzyme dehydrogenase complex, that for pyruvate. Mixing experiments indicated that the abnormality of KGDHC activity in FAD fibroblasts was not due to an inhibitor or to excess protease activity. KGDHC is a complex of three proteins. Immunoblots for the E2k component under conditions of optimal protease inhibition revealed the expected 46-kd species in both AD and non-AD fibroblasts, but the patient cells also regularly contained an additional 29-kd species that was absent or present in minimal amounts in the controls. Immunoblotting demonstrated no abnormalities in the E1k and E3 components. Other studies indicate that the human gene for E2k residues on chromosome 14q24.3, in a region associated with FAD in a number of families including the KGDHC-deficient Nova Scotia kindred. The persistence of abnormalities in KGDHC and particularly in its E2k component in FAD fibroblasts indicates that abnormalities of this autosomally coded nuclear component are an intrinsic part of the AD process, and the possible role of this abnormality in the pathogenesis of AD is discussed.

2-Ketoglutarate dehydrogenase deficiency, a rare cause of primary hyperlactataemia: report of a new case

Two new familial cases of 2-ketoglutarate dehydrogenase (2-KGD) deficiency are reported: a girl who died at 10 years and a boy, still alive at 4 years, born to consanguineous parents. The cases developed progressively severe encephalopathy with axial hypotonia, psychotic behaviour, pyramidal symptoms and failure to thrive. Both children exhibited permanent lactic acidosis with acute episodes during emotional stress and various infections, associated with elevated lactate/pyruvate (L/P) ratio and slightly decreased ketone body ratio in plasma. In fibroblasts, the L/P ratio was greatly increased in the boy. No respiratory chain complex deficiency could be demonstrated in cultured fibroblasts or in mitochondria isolated from a muscle biopsy performed on the boy. In muscle isolated mitochondria, a progressive decrease of the rate of glutamate oxidation was observed after ADP addition; the rate of 2-ketoglutarate oxidation was low in the absence of ADP and did not increase after ADP addition. 2-KGD deficiency was demonstrated in fibroblasts from both children and in the boy's muscle and myoblasts. The 2-KGD complex is composed of three separate enzymes: E1, E2 and E3. We could demonstrate in our patient that the E1 and E3 subunits were normal, suggesting that the E2 component could be responsible for the defect.

Alpha-ketoglutarate dehydrogenase deficiency presenting as congenital lactic acidosis

We report an inborn error of the tricarboxylic acid cycle, alpha-ketoglutarate dehydrogenase deficiency, in three siblings with hypotonia, metabolic acidosis, and hyperlactatemia immediately after birth. Neurologic deterioration resulted in death at about 30 months of age. We propose low molar ratios of ketone bodies in plasma of neonates with congenital lactic acidosis as an indication of dysfunction of the tricarboxylic acid cycle.

Diabetes mellitus, thiamine-dependent megaloblastic anemia, and sensorineural deafness associated with deficient alpha-ketoglutarate dehydrogenase activity

Three brothers with diabetes mellitus, thiamine-responsive megaloblastic anemia, and sensorineural deafness are reported. Two had, in addition, congenital septal defects. The activities of thiamine-dependent enzymes were determined in one patient, revealing low alpha-ketoglutarate dehydrogenase activity, which could have caused a sideroblastic anemia with secondary megaloblastic changes. The anemia was thiamine dependent. The cause of the diabetes mellitus was not known, but it was not type 1.

The inherited ataxias

Diagnosis and classification of the inherited ataxias are reviewed with emphasis on recognizing treatable disorders. Even when basic defects are untreatable, many complications of the degenerative process are amenable to therapy.

A familial progressive neurodegenerative disease with 2-oxoglutaric aciduria

A boy and a girl born to a consanguineous Tunisian couple are suffering from a slowly progressive nervous disorder. Initially they both had normal psychomotor development with acquisition of gait and speech. First symptoms in the boy were athetoid movements during the second year of life. He later lost all motor and language skills and developed muscular rigidity and intention tremor. At the age of five years, he was completely bedridden while he appeared mentally much less affected. His younger sister followed a similar course. The major specific abnormality detected was a strikingly elevated excretion of 2-oxoglutaric acid, which was identified by gas liquid chromatography, mass spectrometry, and enzymatic analysis. 2-oxoglutarate dehydrogenase activity in homogenates of cultured skin fibroblasts was reduced to about 25% of control values in both children. Although the pathogenetic mechanisms leading to brain damage remain obscure, the finding strongly suggest an autosomal recessive neurometabolic disease with predominant involvement of the extrapyramidal system.

Hyperlysinemia with saccharopinuria due to combined lysine-ketoglutarate reductase and saccharopine dehydrogenase deficiencies presenting as cystinuria

A 7-year-old boy with speech delay, hyperactive behavior, and minor neurologic abnormalities had been found in the past to have "intermittent cystinuria." A more detailed investigation revealed hyperlysinemia and hyperlysinuria, with lesser increases in urinary excretion of arginine and cystine. The plasma and urine abnormalities increased on a diet of 3 gm of protein/kg body weight/day. Saccharopine, a normal metabolite of lysine not found in the body fluids of normal people, was present in plasma, cerebrospinal fluid, and urine of the patient. Lysine-ketoglutarate reductase and saccharopine dehydrogenase activities were not detectable in extracts of cultured skin fibroblasts. Re-examination of the urine of previously studied cases of this double enzyme deficiency suggests that saccharopinuria of variable degree is the rule and not the exception.

Pyruvate dehydrogenase deficiency in spinocerebellar degenerations

To study the incidence of abnormalities of the pyruvate (PDH) or ketoglutarate (KGDH) dehydrogenase complexes in patients with spinocerebellar degenerations, we measured the activities of PDH and KGDH in platelet-enriched preparations from the blood of 14 patients. Low PDH was found in 6 of the 14 patients; low KGDH was found in 2 of the 6. PDH-normal and PDH-abnormal patients could not be distinguished by clinical criteria. These results extend previous studies, which suggested abnormalities of pyruvate oxidation in patients with hereditary ataxias. The data imply that deficient activity of the PDH complex may be associated with spinocerebellar degenerations, and that the clinical phenotypes of the inherited ataxias can be associated with several genotypes.

Deficiency of dihydrolipoyl dehydrogenase (a component of the pyruvate and alpha-ketoglutarate dehydrogenase complexes): a cause of congenital chronic lactic acidosis in infancy

A male child died at 7 months of age with progressive neurologic deterioration and persistent metabolic acidosis. Investigations during life showed this child to have elevated blood pyruvate, lactate, and alpha-ketoglutarate as well as elevation of branched chain amino acids and occasional hypoglycemia. Cofactor therapy using either thiamine-HCl (2 g/kg/24 hr) or thiamine tetrahydrofurfuryl disulfide had no measurable effect on the clinical or biochemical status of the patient. Tissue taken postmortem showed normal levels of key gluconeogenic enzymes but a deficiency in the activity of pyruvate dehydrogenase in all tissues tested (liver, brain, kidney, skeletal muscle, and heart). Examination of the individual activities of pyruvate dehydrogenase complex showed pyruvate decarboxylase (E1) to be normal in liver and other tissues. Dihydrolipoyl dehydrogenase (E3), on the other hand, was deficient in all tissues tested. alpha-Ketoglutarate dehydrogenase complex, which depends of E3 for its total activity, was also deficient in all tissues tested. The absence of this enzyme id discussed in relation to the clinical and biochemical status of the patient.

Rapid diagnosis of pyruvate and ketoglutarate dehydrogenase deficiencies in platelet-enriched preparations from blood

Radiochemical methods are described in detail to measure the activities of the pyruvate dehydrogenase complex and of the ketoglutarate dehydrogenase complex in platelet-enriched fractions. Determinations can be completed in one day with as little as 5 ml of venous blood. Activities are proportional to the length of the incubation and the amount of tissue protein added, show appropriate dependence on added cofactors, are stable for up to 2 days at -20 degrees C, and do not appear to be affected by diet. The pyruvate dehydrogenase complex appears to be fully activated (dephosphorylated) in these preparations. Activities were comparable in platelet-enriched fractions from 25 normal subjects and 25 patients with a variety of neurological and psychiatric diagnoses. Mean values (+/- S.E.M.) for these 50 individuals were 169+/-9 pmol/min per mg protein for the pyruvate dehydrogenase complex and 535+/-27 pmol/min per mg protein for the ketoglutarate dehydrogenase complex. These values are comparable to those found in cultured skin fibroblast with similar techniques. Deficient pyruvate dehydrogenase activity (19+/-6 and 11+/-4 pmol/min per mg protein) was demonstrated in platelet-enriched preparations from two brothers whose fibroblasts had previously been shown to be deficient in pyruvate dehydrogenase and who responed to a ketogenic diet. Experimental detail critical to obtaining reproducible results with these methods are stressed (notably the crucial importance of maintaining the purity of the radioactive substrates). These techniques allow identification of patients with pyruvate dehydrogenase deficiencies within one day without requiring liver or muscle biopsy.

Lactic acidosis in three sibs due to defects in both pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes

A Canadian Indian family is described in which three of the children were mentally retarded, and had seizures and other neurological abnormalities. They had chronic metabolic acidosis associated with elevated blood levels of lactate, pyruvate, and alanine. Two of the children excreted large amounts of pyruvic and alpha-ketoglutaric acids in the urine and had elevated plasma levels of glutamic acid and proline. Hypoglycemia occurred with fasting in two of the children. Treatment with pharmacological doses of thiamine, lipoic acid, biotin, riboflavin, and various dietary regimes was without effect. One child died at 3 1/2 months and another at 4 1/2 months; the third is still alive at 23 months of age. Enzyme assays revealed a low level of activity of both the pyruvate and alpha-ketoglutarate dehydrogenase complexes in cultured fibroblasts of one of the sibs. These patients appeared to have partial defects in the oxidation of pyruvate, as well as of alpha-ketoglutarate within the tricarboxylic acid cycle.