3-hydroxyglutaric Acid Research Articles

Glutaric aciduria types I and II

Glutaric aciduria type I is an autosomal recessive disorder resulting from a deficiency of glutaryl-CoA dehydrogenase. This leads to an accumulation of glutaric and 3-hydroxyglutaric acids and secondary carnitine deficiency. The symptomatology is discussed, especially those resulting from lesions in the basal ganglia, and the encephalopathic episodes which are often precipitated by infections. The variability of the clinical presentation is stressed. The most serious complications are collections of fluid and blood in the middle fossae, the bleeding resulting from rupture of bridging veins. The prognosis does not seem to be related to the extent of the enzyme deficiency. The diagnosis is confirmed by identifying the abnormal acids in the urine and the deficiency of the enzyme in cultured fibroblasts. The differential diagnosis is reviewed: from other biochemical disorders and from other cerebral lesions. Treatment is by special diet and carnitine supplementation. The dystonia can prove difficult to treat, and surgery may be needed to remove the collections of fluid and blood. Glutaric aciduria type II is caused by a deficiency of either electron transport flavoprotein or of electron transport flavoprotein oxoreductase. The symptoms can be mild or severe. The former may only occur in times of stress, and the latter include congenital anomalies, especially of the kidneys and heart. The pathology of these are discussed. The demonstration of organic acids in the urine and the results of muscle and liver biopsies confirm the diagnosis, and treatment with a special diet and supplementation with carnitine and riboflavine is effective.

Quinolinic acid reduces the antioxidant defenses in cerebral cortex of young rats

Quinolinic acid (QA), the major metabolite of the kynurenine pathway, is found at increased concentrations in brain of patients affected by various common neurodegenerative diseases, including Huntington's disease and Alzheimer's disease. Recently, a role for QA in the pathophysiology of glutaric acidemia type I (GAI) was postulated. Considering that oxidative stress has been recently involved in the pathophysiology of the brain injury in these neurodegenerative disorders; in the present study, we investigated the in vitro effect of QA on various parameters of oxidative stress, namely total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR), glutathione (GSH) levels, thiobarbituric acid-reactive substances (TBA-RS) measurement and chemiluminescence in cerebral cortex of 30-day-old rats. QA diminished the brain non-enzymatic antioxidant defenses, as determined by the reduced levels of TRAP, TAR and GSH. We also observed that QA significantly increased TBA-RS and chemiluminescence. Therefore, in vitro QA-treatment of rat cortical supernatants induced oxidative stress by reducing the tissue antioxidant defenses and increasing lipid oxidative damage, probably as a result of free radical generation. In addition, we examined the effect of QA on TBA-RS levels in the presence of glutaric acid (GA) and 3-hydroxyglutaric acid (3HGA), which are accumulated in GAI, as well as in the presence of 3-hydroxykynurenine (3HK), a tryptophan metabolite of the kynurenine pathway with antioxidant properties. It was verified that the single addition of QA or GA plus 3HGA to the incubation medium significantly stimulated in vitro lipid peroxidation. Furthermore, 3HK completely prevented the TBA-RS increase caused by the simultaneous addition of QA, GA and 3HGA. Taken together, it may be presumed that QA induces oxidative stress in the brain, which may be associated, at least in part, with the pathophysiology of central nervous system abnormalities of neurodegenerative diseases in which QA accumulates.

Novel metabolic and molecular findings in hepatic carnitine palmitoyltransferase I deficiency

Detection of hepatic carnitine palmitoyltransferase I (CPT IA) deficiency by metabolite screening may be problematic. The urine organic acid profile is generally said to be normal and no abnormal or increased acylcarnitine species are evident on bloodspot tandem MS examination. We diagnosed CPT IA deficiency presenting with acute encephalopathy +/− hypoglycemia and hepatomegaly in one Bukharan Jewish and two Palestinian Arab infants from consanguineous families. CPT1A mutation analysis identified two novel nonsense mutations, c.1737C > A (Y579X) and c.1600delC (L534fsX), extending the known genetic heterogeneity in this disorder. A distinctive organic aciduria was observed in all three patients, even several days after initiation of treatment and resolution of symptoms. Abnormal findings included a hypoketotic dicarboxylic aciduria with prominence of the C 12 dicarboxylic (dodecanedioic) acid. This C 12 dicarboxylic aciduria suggests that CPT I may play a role in uptake of long-chain dicarboxylic acids by mitochondria after their initial shortening by β-oxidation in peroxisomes. In addition, increased excretion of 3-hydroxyglutaric acid was detected in all three patients, a finding previously observed only in glutaric aciduria type 1, ketosis, and short-chain hydroxyacyl-CoA dehydrogenase deficiency. Examination of urine organic acids with awareness of these metabolic findings may lead to improved diagnosis of this seemingly rare disorder.

Glutaric Aciduria Type I: A Neuroimaging Diagnosis?

Glutaric aciduria type I is an autosomal recessive disorder of organic acid metabolism secondary to glutaryl-coenzyme A (CoA) dehydrogenase deficiency. We report a previously healthy 17-month-old girl who presented with acute dystonia. Conventional T2-weighted and fluid-attenuated inversion recovery magnetic resonance images of the brain showed hyperintensity in the caudates and putamina bilaterally with subtle involvement of the medial frontal lobes. Diffusion-weighted magnetic resonance images showed striking restricted diffusion in the caudates and putamina consistent with acute necrosis. Single-voxel hydrogen magnetic resonance spectroscopy of the involved areas was normal. The clinical diagnosis of glutaric aciduria type I was confirmed by elevation of 3-hydroxyglutaric and glutaric acids. Diffusion-weighted magnetic resonance imaging is a sensitive indicator of basal ganglia necrosis in glutaric aciduria type I.

Quantification of glutaric and 3-hydroxyglutaric acids in urine of glutaric acidemia type I patients by HPLC with intramolecular excimer-forming fluorescence derivatization

Background Glutaric aciduria type I (GA1) is an autosomal recessive disorder that usually causes neurological damage. Early diagnosis of the disease prior to the appearance of clinical symptoms can lead to better outcomes. Methods We describe a simple and selective HPLC method with intramolecular excimer-forming fluorescence derivatization to diagnose GA1. Glutaric acid (GA) and 3-hydroxyglutaric acid (3HGA) in urine and an internal standard were derivatized with 1-pyrenebutyric hydrazide (PBH). The derivatives were separated on a C 18 column and fluorometrically detected at 475 nm (excitation of 345 nm) with a run time of 18 min. Results Excellent linearity over a wide range, reproducibility (coefficient of variation ≤ 14.5%), and sensitivity (limit of detection 0.4 μmol/l 3HGA and 0.2 μmol/l GA) were obtained. A retrospective study on previously diagnosed GA1 patients' urine from our laboratory archives between 1999 and 2004 was performed by analysts blinded to the study. Conclusions The method enabled us to differentiate GA1 cases ( n = 36) from controls ( n = 99), regardless of the years of urine storage. The method is valuable for both retrospective and prospective diagnoses of GA1.

Bioenergetics in Glutaryl-Coenzyme A Dehydrogenase Deficiency: A ROLE FOR GLUTARYL-COENZYME A

Inherited deficiency of glutaryl-CoA dehydrogenase results in an accumulation of glutaryl-CoA, glutaric, and 3-hydroxyglutaric acids. If untreated, most patients suffer an acute encephalopathic crisis and, subsequently, acute striatal damage being precipitated by febrile infectious diseases during a vulnerable period of brain development (age 3 and 36 months). It has been suggested before that some of these organic acids may induce excitotoxic cell damage, however, the relevance of bioenergetic impairment is not yet understood. The major aim of our study was to investigate respiratory chain, tricarboxylic acid cycle, and fatty acid oxidation in this disease using purified single enzymes and tissue homogenates from Gcdh-deficient and wild-type mice. In purified enzymes, glutaryl-CoA but not glutaric or 3-hydroxyglutaric induced an uncompetitive inhibition of alpha-ketoglutarate dehydrogenase complex activity. Notably, reduced activity of alpha-ketoglutarate dehydrogenase activity has recently been demonstrated in other neurodegenerative diseases, such as Alzheimer, Parkinson, and Huntington diseases. In contrast to alpha-ketoglutarate dehydrogenase complex, no direct inhibition of glutaryl-CoA, glutaric acid, and 3-hydroxyglutaric acid was found in other enzymes tested. In Gcdh-deficient mice, respiratory chain and tricarboxylic acid activities remained widely unaffected, virtually excluding regulatory changes in these enzymes. However, hepatic activity of very long-chain acyl-CoA dehydrogenase was decreased and concentrations of long-chain acylcarnitines increased in the bile of these mice, which suggested disturbed oxidation of long-chain fatty acids. In conclusion, our results demonstrate that bioenergetic impairment may play an important role in the pathomechanisms underlying neurodegenerative changes in glutaryl-CoA dehydrogenase deficiency.

Stable-isotope dilution gas chromatography–mass spectrometric measurement of 3-hydroxyglutaric acid, glutaric acid and related metabolites in body fluids of patients with glutaric aciduria type 1 found in newborn screening

We developed a simple and sensitive stable-isotope dilution method for the quantification of 3-hydroxyglutaric acid (3HGA) and glutaric acid (GA) in body fluids. In our method, tert-butyldimethylsilyl (tBDMS) derivatives of 3HGA and GA were measured with a conventional electron-impact ionization (EI) mode in gas chromatography–mass spectrometry (GC–MS). The control values for 3HGA in nmol/ml were 0.15 ± 0.08 (serum; n = 10) and 0.07 ± 0.03 (CSF; n = 10). In addition, glutarylcarnitine and free carnitine were quantified by electrospray tandem mass spectrometry. Using these methods, we monitored 3HGA, GA, and glutarylcarnitine in the body fluids of three patients with glutaric aciduria type 1 found during newborn screening. None of the patients had experienced neurological strokes, which are possibly caused by the accumulation of 3HGA, at 15–24 months of age under a disease-specific treatment, including carnitine supplementation. Our data showed that 3HGA levels were relatively high in some serum samples with lower glutarylcarnitine and carnitine levels, suggesting that carnitine supplementation may play a role in preventing the accumulation of 3HGA in patients with this disease.

Diagnosis Of Glutaric Acidemia Type I: A Cautionary Note

� Glutaric acidemia type I (GA-I) is a progressive neurodegenerative disease caused by a deficiency of glutaryl-CoA dehydrogenase (GCDH) and accumulation of glutaric, glutaconic, and 3hydroxyglutaric acids in an affected patient’s urine. � Tandem mass spectrometry (MS/MS)-based detection of glutarylcarnitine in dried bloodspots forms the basis for screening for GA-I in asymptomatic individuals. The presence of normal levels of plasma glutarylcarnitine in asymptomatic individuals with GA-I deficiency may be falsely reassuring because urine glutarylcarnitine levels may be elevated in these individuals. � Measurement of urinary glutarylcarnitine levels by MS/MS should be part of the screening and diagnostic protocol for identifying individuals with GA-I, especially in populations with a high incidence of GAI, because these patients may benefit from early diagnosis and the introduction of dietary management during the presymptomatic stage of this disease.

Promotion of oxidative stress by 3‐hydroxyglutaric acid in rat striatum

The pathophysiology of the striatum degeneration characteristic of patients affected by the inherited neurometabolic disorder glutaryl-CoA dehydrogenase deficiency (GDD), also known as glutaric aciduria type I, is still in debate. We have previously reported that 3-hydroxyglutaric acid (3-OH-GA) considered the main neurotoxin in this disorder, induces oxidative stress in rat cerebral cotex. In the present work, we extended these studies by investigating the in vitro effect of 3-OH-GA, at concentrations ranging from 0.01 to 1.0 mmol/L on the brain antioxidant defences by measuring total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR) and glutathione (GSH) levels, and on the production of hydrogen peroxide (H(2)O(2)), nitric oxide (NO) and malondialdehyde in striatum homogenates from young rats. We observed that TRAP, TAR and GSH levels were markedly reduced (by up to 50%) when striatum homogenates were treated with 3-OH-GA. In contrast, H(2)O(2) (up to 44%), NO (up to 95%) and malondialdehyde levels (up to 28%) were significantly increased by 3-OH-GA. These data indicate that total nonenzymatic antioxidant defences (TRAP) and the tissue capacity to handle an increase of reactive species (TAR) were reduced by 3-OH-GA in the striatum. Furthermore, the results also reflect an increase of lipid peroxidation, probably secondary to 3-OH-GA-induced free radical production. Thus, it may be presumed that oxidative stress is involved in the neuropathology in GDD.

3-Hydroxyglutaric acid moderately impairs energy metabolism in brain of young rats

3-Hydroxyglutaric acid (3HGA) accumulates in the inherited neurometabolic disorder known as glutaryl-CoA dehydrogenase deficiency. The disease is clinically characterized by severe neurological symptoms, frontotemporal atrophy and striatum degeneration. Because of the pathophysiology of the brain damage in glutaryl-CoA dehydrogenase deficiency is not completed clear, we investigated the in vitro effect of 3HGA (0.01–5.0mM) on critical enzyme activities of energy metabolism, including the respiratory chain complexes I–V, creatine kinase isoforms and Na +,K +-ATPase in cerebral cortex and striatum from 30-day-old rats. Complex II activity was also studied in rat C6-glioma cells exposed to 3HGA. The effect of 3HGA was further investigated on the rate of oxygen consumption in mitochondria from rat cerebrum. We observed that 1.0mM 3HGA significantly inhibited complex II in cerebral cortex and C6 cells but not the other activities of the respiratory chain complexes. Creatine kinase isoforms and Na +,K +-ATPase were also not affected by the acid. Furthermore, no inhibition of complex II activity occurred when mitochondrial preparations from cerebral cortex or striatum homogenates were used. In addition, 3HGA significantly lowered the respiratory control ratio in the presence of glutamate/malate and succinate under stressful conditions or when mitochondria were permeabilized with digitonin. Since 3HGA stimulated oxygen consumption in state IV and compromised ATP formation, it can be presumed that this organic acid might act as an endogenous uncoupler of mitochondria respiration. Finally, we observed that 3HGA changed C6 cell morphology from a round flat to a spindle-differentiated shape, but did not alter cell viability neither induced apoptosis. The data provide evidence that 3HGA provokes a moderate impairment of brain energy metabolism and do not support the view that 3HGA-induced energy failure would solely explain the characteristic brain degeneration observed in glutaryl-CoA dehydrogenase deficiency patients.

Glutaconyl-CoA is the main toxic agent in glutaryl-CoA dehydrogenase deficiency (glutaric aciduria type I)

Despite early diagnosis and treatment, 35% of the patients with glutaric aciduria type I (GA I) develop severe neurologic damage. Glutaric acid and 3-hydroxyglutaric acid have been suspected to cause neurodegeneration. Lately, this has been questioned, however. We postulate that glutaconyl Coenzyme A (glutaconyl-CoA) is responsible for brain damage. Chemically, glutaconyl-CoA is an analogue of acrylyl-CoA, the parent substance of the extremely reactive class of acrylates. It is expected to react spontaneously with sulfhydryl groups, thus modifying membranes, disturbing enzyme functions and trapping glutathione. Enhanced production of glutaconyl-CoA together with lack of glutathione precipitates brain damage. Such a mechanism is supported by three findings. (1) The addition product of glutaconyl-CoA to cysteine is present in small amounts in normal human urine. (2) Reaction of methacrylyl-CoA with free sulfhydryl groups has been reported previously in a patient with 3-hydroxyisobutyryl CoA deacylase deficiency. (3) Glutathione has been found to be decreased in homozygous glutaryl-CoA dehydrogenase-deficient knock-out mice.

The urinary excretion of glutarylcarnitine is an informative tool in the biochemical diagnosis of glutaric acidemia type I

Glutaric acidemia type I (GA-1) is a progressive neurodegenerative inborn error of metabolism that typically manifests acutely in infants during an intercurrent illness. The diagnosis is established biochemically by the detection of glutaric acid and 3-hydroxy glutaric acid in urine and glutarylcarnitine in plasma. However, some patients excrete only small amounts of glutaric acid and may be overlooked, especially if the plasma concentration of glutarylcarnitine is not elevated. To test the hypothesis that measuring the excretion of glutarylcarnitine may improve the recognition of GA-1 patients without significant glutaric aciduria, urine glutarylcarnitine was analyzed in 14 cases. Five of them lacked significant glutaric aciduria, 9 (of 10 available) had a normal plasma glutarylcarnitine concentration. As controls, we also evaluated 54 subjects with glutaric aciduria secondary to other causes (16–7509 mmol/mol creatinine; reference range: <15; no significant amounts of 3-hydroxy glutaric acid detectable). The excretion of glutarylcarnitine was significantly elevated in all GA-1 patients (14–522 mmol/mol creatinine; reference range: <5.2) and in none of the controls with glutaric aciduria. These findings suggest that the urinary excretion of glutarylcarnitine is a specific biochemical marker of GA-1 which could be particularly useful in the work up of patients with suggestive clinical manifestations but without glutaric aciduria and with normal plasma acylcarnitine profiles.

Excitotoxicity and bioenergetics in glutaryl‐CoA dehydrogenase deficiency

Glutaryl-CoA dehydrogenase deficiency is an inherited organic acid disorder with predominantly neurological presentation. The biochemical hallmark of this disease is an accumulation and enhanced urinary excretion of two key organic acids, glutaric acid and 3-hydroxyglutaric acid. If untreated, acute striatal damage is often precipitated by febrile illnesses during a vulnerable period of brain development in infancy or early childhood, resulting in a dystonic dyskinetic movement disorder. 3-hydroxyglutaric and glutaric acids are structurally similar to glutamate, the main excitatory amino acid of the human brain, and are considered to play an important role in the pathophysiology of this disease. 3-hydroxyglutaric acid induces excitotoxic cell damage specifically via activation of N-methyl-D-aspartate receptors. It has also been suggested that secondary amplification loops potentiate the neurotoxic properties of these organic acids. Probable mechanisms for this effect include cytokine-stimulated NO production, a decrease in energy metabolism, and reduction of cellular creatine phosphate levels. Finally, maturation-dependent changes in the expression of neuronal glutamate receptors may affect the vulnerability of the immature brain to excitotoxic cell damage in this disease.

Preliminary attempts to establish a rat model of striatal injury in glutaric acidaemia type I

Glutaric acidaemia type I (GA I) is caused by the deficiency of glutaryl-CoA dehydrogenase, resulting in accumulation of glutaric acid (GA) and 3- hydroxyglutaric acid (3-OH-GA) in blood and cerebrospinal fluid (CSF). Neuropathological changes with onset in childhood consist of severe neuronal loss in the caudate and putamen. An animal model is necessary to test possible intervention strategies, and prior reports suggested that GA or 3-OH-GA could be used to create specific neuron loss in adult rats. Adult, 3-week-old and 2-week-old rats received intrastriatal injections of GA and 3-OH-GA at a range of doses. High concentrations caused necrotic lesions in striatum. Low concentrations caused white-matter axonal damage and small areas of neuron loss. Injection of lipopolysaccharide prior to administration of 3-OH-GA was not associated with enhanced neuronal loss. Our findings contradict prior claims and we conclude that the simple model of a single GA or 3-OH-GA injection into rat brain does not replicate the neuropathological findings in humans.

Modulation of glutamatergic and GABAergic neurotransmission in glutaryl‐CoA dehydrogenase deficiency

Although the precise mechanisms underlying the CNS degeneration of patients with glutaryl-CoA dehydrogenase (GCDH) deficiency are still the subject of intense debate, many studies have highlighted that excitotoxicity plays a fundamental role in the neuropathology of this disease, particularly involving the N-methyl-D-aspartate receptor subtype of ionotropic glutamate receptors. Modulation of the glutamatergic system by these compounds involves an inhibition of glutamate uptake into synaptosomes and synaptic vesicles, and a decrease in glutamate binding. Furthermore, glutaric and 3-hydroxyglutaric acids inhibit glutamate decarboxylase, the key enzyme of GABA synthesis, and striatal GABAergic medium-spiny neurons are highly vulnerable to 3-hydroxyglutaric acid-induced neurotoxicity. In conclusion, glutaric acid and 3-hydroxyglutaric acid induce an imbalance in glutamatergic and GABAergic neurotransmission.

Glutaric aciduria type I and kynurenine pathway metabolites: A modified hypothesis

Glutaric aciduria type I is an inborn error of organic acid metabolism that demonstrates a particular temporal vulnerability (acute encephalopathic episodes in infancy) and a spatial vulnerability (acute striatal necrosis, focused on the putamen). Excitotoxic mechanisms involving 3-hydroxyglutaric acid as the major neurotoxin have been suggested. This paper proposes a role for metabolites of the kynurenine pathway in the pathogenic process and modifies the hypothesis of Heyes. Deficiency of glutaryl-CoA dehydrogenase blocking the glutarate pathway and activation of indoleamine 2,3-dioxygenase in macrophages/monocytes by intercurrent inflammation may increase flux down the kynurenine pathway towards the production of quinolinic acid. Quinolinic acid is neurotoxic and is an endogenous agonist at N-methyl-D-aspartate receptors. Synergistic excitation of these receptors by quinolinic acid and 3-hydroxyglutaric acid, which alone does not have sufficient potency, may be involved in the pathogenesis of striatal necrosis.

Challenges for basic research in glutaryl‐CoA dehydrogenase deficiency

During the last decades, efforts have been made to elucidate the complex mechanisms underlying neuronal damage in glutaryl-CoA dehydrogenase deficiency. A combination of in vitro and in vivo investigations have facilitated the development of several hypotheses, including the probable pathogenic role of accumulating glutaric acid and 3-hydroxyglutaric acid. However, there are still many shortcomings that limit an evidence-based approach to treating this inborn error of metabolism. Major future goals should include generation of a suitable animal model for acute striatal necrosis, investigation of the formation, distribution and exact intra- and extracellular concentrations of accumulating metabolites, a deeper understanding of striatal vulnerability, and systematic investigation of effects on cerebral gene expression during development and of the modulatory role of inflammatory cytokines.

Reduction of lysine intake while avoiding malnutrition—Major goals and major problems in dietary treatment of glutaryl‐CoA dehydrogenase deficiency

Treatment in glutaryl-CoA dehydrogenase deficiency, an inborn error of metabolism of lysine and tryptophan, is mainly based on restriction of lysine intake, supplementation of carnitine, and an intensification of therapy during intercurrent illnesses. The major principle of dietary treatment is to reduce the production of glutaric acid and 3-hydroxyglutaric acid by restriction of natural protein in general and of lysine in particular. In parallel to development, the growing child learns to utilize different protein sources, shifting the primarily milk-based diet to a mixed diet. The changes in nutritional demands and food composition during the first years of life greatly influence nutritional support for affected patients at different ages. This article highlights frequent pitfalls of dietary treatment for this disease and focuses on particular risks of malnutrition in terms of essential amino acids and micronutrients and/or excess intake of lysine between age 3 months and age 6 years. We conclude from the examples given that restriction of natural protein intake plus application of lysine-free amino acid mixtures minimizes the risk of malnutrition and allows a reliable control of protein and lysine intake and, thus, seems particularly recommendable during the vulnerable period for acute encephalopathic crises. The efficacy of these theoretical and experience-based approaches to dietary treatment of glutaryl-CoA dehydrogenase deficiency should be investigated in detail in prospective clinical studies.

Animal models for glutaryl‐CoA dehydrogenase deficiency

In vitro studies suggest that excitotoxic cell damage is an underlying mechanism for the acute striatal damage in glutaryl-CoA dehydrogenase (GCDH) deficiency. It is believed to result from an imbalance of glutamatergic and GABAergic neurotransmission induced by the accumulating organic acids 3-hydroxyglutaric acid (3-OH-GA) and to a lesser extent glutaric acid (GA). Stereotaxic administration of 3-OH-GA and GA into the rat striatum have confirmed these results, but may not truly represent the effect of chronic exposure to these compounds. In an attempt to better understand the pathophysiology of GCDH deficiency in vivo , two animal models have been utilized. A mouse that lacks GCDH activity in all tissues was generated by gene targeting in embryonic stem cells. These animals develop the characteristic biochemical phenotype of the human disease. Pathologically, these mice have a diffuse spongiform myelinopathy similar to that in human patients; however, there is no evidence for acute striatal damage or sensitivity to acute encephalopathy induced by catabolism or inflammatory cytokines. A naturally occurring animal model, the fruit-eating bat Rousettus aegypticus, lacks hepatic and renal GCDH activity, but retains cerebral enzyme activity. Like the mouse, these bats develop the characteristic biochemical phenotype of glutaryl-CoA dehydrogenase deficiency, but lack overt neurological symptoms such as dystonia. It is not known whether they also develop the spongiform myelinopathy seen in the Gcdh-deficient mice. Otherwise, these constellations would suggest that cerebral GCDH deficiency is responsible for the development of neuronal damage. The lack of striatal damage in these two rodent models may also be related to species differences. However, they also highlight our lack of a comprehensive understanding of additional factors that might modulate the susceptibiliy of neurons to accumulating 3-OH-GA and GA in GCDH deficiency. Unravelling these mechanisms may be the key to understanding the pathophysiology of this unique disease and to the development of neuroprotective strategies.

Correlation of genotype and phenotype in glutaryl‐CoA dehydrogenase deficiency

We have investigated the correlation between genotype and phenotype in a large number of patients with glutaric aciduria type I (GA I). The deficiency of glutaryl-CoA dehydrogenase has been confirmed in the Rigshospitalet's laboratory in 215 patients since 1975. Most of the patients were of European ancestry. Complete absence of enzyme activity was found in more than half of the patients, while 34% of patients had a residual activity up to 5% and a few patients had a residual activity of 5-15%. In four exceptional cases, a very high residual activity of up to 30% was found. Enzyme studies are thus a reliable method for confirming the diagnosis of GA I, although it may be difficult to distinguish exceptional 'mild' cases from heterozygous carriers for GA I. Three of the patients with very high residual activity are compound heterozygous for the missense mutations R227P and V400M, both of which are associated with residual enzyme activity of 8-10% in homozygous patients. Patients with a mild mutation on at least one chromosome frequently show unusual biochemical findings such as low or normal urinary excretion of glutaric acid and mild or only slightly increased excretion of 3-hydroxyglutaric acid. In contrast, patients with severe mutations such as R402W or A293T on both alleles have no residual activity and show the typical urinary metabolite pattern. Clinical data were available for a subgroup of 79 patients. No correlation with the biochemical phenotype or the genotype could be established.