D-2-hydroxyglutaric aciduria: further clinical delineation

L-2-Hydroxyglutaric aciduria in Staffordshire Bull Terriers

L-2-Hydroxyglutaric aciduria is an inborn error of metabolism, which has been recognized in humans since 1980. The metabolic defect responsible for the disease is unknown, but the disorder can be diagnosed in humans by elevations of the organic acid, L-2-hydroxyglutaric acid in the cerebrospinal fluid (CSF), plasma, and urine of affected patients. The disorder produces a variety of clinical neurological defects in humans including psychomotor retardation, seizures, and ataxia. There have previously been no recognized animal models of the disease. However, 6 Staffordshire Bull Terriers were recently identified with the disorder. The animals presented with a variety of clinical signs, most notably seizures, ataxia, dementia, and tremors. They were all screened for organic acid abnormalities in urine, and CSF and plasma (when available). Levels of L-2-hydroxyglutaric acid were elevated in all body fluids evaluated. The clinical, clinicopathologic, and magnetic resonance imaging (MRI) characteristics associated with L-2-hydroxyglutaric acid in Stafforshire Bull Terriers is reported herein and represents the first veterinary model of this inborn error of metabolism.

D-2-hydroxyglutaric acid induces oxidative stress in cerebral cortex of young rats

Large amounts of d-2-hydroxyglutaric acid (DGA) accumulate in d-2-hydroxyglutaric aciduria (D-2-OHGA), an inherited neurometabolic disorder characterized by severe neurological dysfunction and cerebral atrophy. Despite the significant brain abnormalities, the neurotoxic mechanisms of brain injury in this disease are virtually unknown. In this work, the in vitro effect of DGA on various parameters of oxidative stress was investigated; namely chemiluminescence, thiobarbituric acid-reactive substances (TBA-RS), total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR) and the activities of the antioxidant enzymes catalase, glutathione peroxidase and superoxide dismutase in cerebral cortex from 30-day-old-rats. DGA significantly increased chemiluminescence and TBA-RS and decreased TAR values in the cortical supernatants. In contrast, TRAP and the antioxidant enzyme activities were not altered by the metabolite. Furthermore, the DGA-induced increase of TBA-RS was fully prevented by the free radical scavengers ascorbic acid plus Trolox (water-soluble alpha-tocopherol) and attenuated by the inhibitor of nitric oxide synthase Nomega-nitro-L-arginine methyl ester (L-NAME), suggesting the role of superoxide, hydroxyl and nitric oxide radicals in this action. The data indicate a stimulation of lipid peroxidation through the production of free radicals and a reduction of the brain capacity to efficiently modulate the damage associated with the enhanced generation of free radicals by DGA. In the case that these findings also occur in human D-2-OHGA, it is feasible that oxidative stress may be involved in the pathophysiology of the brain injury observed in patients with this disease.

Spondyloenchondromatosis with D-2-hydroxyglutaric aciduria: a report of a second patient with this unusual combination

Spondyloenchondromatosis (SEM) is a rare skeletal dysplasia which presents with multiple enchondromata in the metaphyses of the long bones associated with dysplastic vertebral bodies. It is probably heterogeneous. We have investigated and documented a male infant in South Africa with spondyloenchondromatosis and persistent D-2-hydroxyglutaric aciduria (D2HA). D2HA is a neurometabolic disorder whose enzymatic basis is still undefined. A girl in England with a similar clinical, radiological and biochemical phenotype has previously been reported by Talkhani et al. [(2000). Skel Radiol 7:215-2921]. There is at present a lack of a plausible pathogenetic relationship between the two components of the disorder but a contiguous gene syndrome or a pleiotropic gene could be considered. Whatever the underlying mechanism this case report confirms its nosological entity.

D-2-Hydroxyglutaric aciduria with absence of corpus callosum and neonatal intracranial haemorrhage

We report D-2-hydroxyglutaric aciduria in a neonate with intracranial haemorrhage and absence of the corpus callosum. D-2-hydroxyglutaric acid was confirmed by specific chiral derivatization gas chromatography-mass spectrometry. Absence of the corpus callosum and spontaneous neonatal intracranial haemorrhage should raise the suspicion for metabolic disease, and especially organic acidurias.

NMDA receptor activation and respiratory chain complex V inhibition contribute to neurodegeneration in d-2-hydroxyglutaric aciduria

The inherited neurometabolic disease d-2-hydroxyglutaric aciduria is complicated by progressive neurodegeneration of vulnerable brain regions during infancy and early childhood, frequently presenting with hypotonia, epilepsy and psychomotor retardation. Here, we report that the pathogenetic role of the endogenously accumulating metabolite d-2-hydroxyglutarate (D-2), which is structurally similar to the excitatory amino acid glutamate, is mediated by at least three mechanisms. (i) D-2-induced excitotoxic cell damage in primary neuronal cultures from chick and rat involved N-methyl-d-aspartate (NMDA) receptor activation. Indeed, D-2 activated recombinant NMDA receptors (NR1/NR2A, NR1/NR2B) but not recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) receptors in HEK293 cells. (ii) Fluorescence microscopy using fura-2 as a calcium indicator and the oxidant-sensitive dye dihydrorhodamine-123 revealed that D-2 disturbed intracellular calcium homeostasis and elicited the generation of reactive oxygen species. (iii) D-2 reduced complex V (ATP synthase) activity of the mitochondrial respiratory chain, reflecting an impaired energy metabolism due to inhibition of ATP synthesis but without affecting the electron-transferring complexes I-IV. Thus, D-2 stimulates neurodegeneration by mechanisms well-known for glutamate, NMDA or mitochondrial toxins. In conclusion, excitotoxicity contributes to the neuropathology of d-2-hydroxyglutaric aciduria, highlighting new neuroprotective strategies.

D-2-Hydroxyglutaric aciduria in a patient with a severe clinical phenotype and unusual MRI findings

We report an infant with intermittent urinary excretion of D-2-hydroxyglutaric (D-2-OHG) acid who died at the age of 10 months from cardiogenic shock due to cardiomyopathy. High urinary concentrations of D-2-OHG and succinic acid, as well as increased levels of lactic acid were detected on three different occasions, whereas a normal urinary profile of organic acids was found on one occasion. The clinical findings of our patient consisted of generalized hypotonia, irritability, developmental delay, generalized tonic seizures, lethargy, cardiomyopathy, and respiratory distress. Cerebral MRI revealed bilateral lesions in the substantia nigra, the periaqueductal area, the medial part of the thalamus, the hypothalamus, the caudate nucleus, putamen and globus pallidus. This pattern is suggestive of a mitochondriopathy. However, respiratory chain enzyme activities were normal in fibroblasts. Exogenous supplementation of D-2-OHG acid strongly inhibited cytochrome-c oxidase activity in fibroblasts from the patient and from normal controls in vitro. The results suggest that our patient has an unusual form of D-2-hydroxyglutaric aciduria (D-2-OHGA), different from the patients published so far, and that the increase of lactic acid and some citric acid cycle intermediates encountered in some patients with D-2-OHGA may be due to a functional defect of the respiratory chain caused by D-2-OHG acid.

Inhibition of cytochrome c oxidase activity in rat cerebral cortex and human skeletal muscle by D-2-hydroxyglutaric acid in vitro

L-2-Hydroxyglutaric (LGA) and D-2-hydroxyglutaric (DGA) acids are the characteristic metabolites accumulating in the neurometabolic disorders known as L-2-hydroxyglutaric aciduria and D-2-hydroxyglutaric aciduria, respectively. Although these disorders are predominantly characterized by severe neurological symptoms, the neurotoxic mechanisms of brain damage are virtually unknown. In this study we have evaluated the role of LGA and DGA at concentrations ranging from 0.01 to 5.0 mM on various parameters of energy metabolism in cerebral cortex slices and homogenates of 30-day-old Wistar rats, namely glucose uptake, CO(2) production and the respiratory chain enzyme activities of complexes I to IV. DGA significantly decreased glucose utilization (2.5 and 5.0 mM) by brain homogenates and CO(2) production (5 mM) by brain homogenates and slices, whereas LGA had no effect on either measurement. Furthermore, DGA significantly inhibited cytochrome c oxidase activity (complex IV) (EC 1.9.3.1) in a dose-dependent manner (35-95%) at doses as low as 0.5 mM, without compromising the other respiratory chain enzyme activities. In contrast, LGA did not interfere with these activities. Our results suggest that the strong inhibition of cytochrome c oxidase activity by increased levels of DGA could be related to the neurodegeneration of patients affected by D-2-hydroxyglutaric aciduria.

D-2-hydroxyglutaric aciduria with cerebral, vascular, and muscular abnormalities in a 14-year-old boy

D-2-Hydroxyglutaric Aciduria is a rare metabolic disorder that can cause injury to the brain and other organs. This case report concerns a 14-year-old boy showing irritability and typical signs of pyloric stenosis early postnatally. From the age of 3 months he had epilepsy. He was mentally retarded, hypotonic with preserved reflexes, and dystonic. The features were dysmorphic with elongated head and high arched palate. Cardiomegaly with aortic insufficiency was diagnosed. Magnetic resonance imaging of the brain revealed atrophy, reduced periventricular white matter, and multiple bilateral aneurysms of the middle cerebral arteries. The boy died at the age of 14 years. Autopsy confirmed the white-matter reduction of the cerebral hemispheres as well as the arterial aneurysms of the middle cerebral arteries. Lesions of a few leptomeningeal and cerebral microvessels and of the renal and pulmonary arteries were also found. There were bilateral infarcts of the kidneys and signs of cardiomyopathy with noncompensated left ventricular failure. Signs of myopathy were evident. The clinical and postmortem findings imply a disseminated mesenchymal process.