Low leukocyte glutamate dehydrogenase activity does not correlate with a particular type of multiple system atrophy

CT Features of Olivopontocerebellar Atrophy in Children

Between 1990 and 1992, 14 children were seen in whom a clinical diagnosis of olivopontocerebellar atrophy (OPCA) had been made. The majority of patients presented with cerebellar ataxia and hypotonia. Five children had a family history of a similar illness in first-degree relatives. All cases had undergone clinical and neurologic examinations, routine laboratory tests and cranial CT. CT features were graded to quantitate the degree of atrophy in each cerebellar hemisphere, vermis and brain stem. All patients had varying degrees of atrophic changes of cerebellum, brain stem and cerebrum. These CT features appear to be distinctive enough to enable the diagnosis of OPCA to be made.

Glutamate Dehydrogenase Deficiency in Cerebellar Degenerations: Clinical, Biochemical and Molecular Genetic Aspects

Glutamate dehydrogenase (GDH), an enzyme central to glutamate metabolism, is significantly reduced in patients with heterogenous neurological disorders characterized by multiple system atrophy (MSA) and predominant involvement of the cerebellum and its connections. In human brain, GDH exists in multiple isoforms differing in their isoelectric point and molecular mass. These are differentially reduced in quantity and altered in catalytic activity in patients with clinically distinct forms of MSA, thus suggesting that these GDH isoproteins are under different genetic control. Dysregulation of glutamate metabolism occurs in patients with GDH deficiency and is thought to mediate the disease’s neurodegeneration via neuroexcitotoxic mechanisms. This possibility is supported by additional data showing that glutamate binding sites are significantly decreased in cerebellar tissue obtained at autopsy from MSA patients. At the molecular biological level, several cDNAs specific for human GDH have been isolated recently and cloned. Northern blot analysis of various human tissues, including brain, has revealed the presence of multiple GDH-specific mRNAs. In addition, multiple GDH-specific genes are present in humans and these data are consistent with the possibility that the various GDH isoproteins are encoded by different genes. These advances have laid the groundwork for characterizing the human GDH genes and their products in health and disease.

A Japanese family with early-onset ataxia with motor and sensory neuropathy

We report the case of a Japanese family with hereditary ataxia with peripheral neuropathy. Three affected siblings from this family exhibited very similar clinical features: teenage-onset, slowly progressive ataxia, followed by distal weakness, which developed after the age of 30 years. Magnetic resonance imaging studies showed marked atrophy in the cerebellar hemisphere and vermis, and a sural nerve biopsy revealed a marked reduction in the number of both myelinated and unmyelinated fibers. All patients exhibited hyperglutamatemia, but serum levels of albumin and lipid were normal. The clinicopathological and biochemical features of these cases suggest that they form a distinct entity of autosomal recessive hereditary ataxia with peripheral neuropathy.

Regulation of human glutamate dehydrogenases: implications for glutamate, ammonia and energy metabolism in brain

Glutamate dehydrogenase (GDH) catalyzes the oxidative deamination of glutamate to alpha-ketoglutarate using NAD or NADP as cofactors. In mammalian brain, GDH is located predominantly in astrocytes, where it is probably involved in the metabolism of transmitter glutamate. The exact mechanisms that regulate glutamate fluxes through this pathway, however, have not been fully understood. In the human, GDH exists in heat-resistant and heat-labile isoforms, encoded by the GLUD1 (housekeeping) and GLUD2 (nerve tissue-specific) genes, respectively. These forms differ in their catalytic and allosteric properties. Kinetic studies showed that the K(m) value for glutamate for the nerve tissue GDH is within the range of glutamate levels in astrocytes (2.43 mM), whereas for the housekeeping enzyme, this value is significantly higher (7.64 mM; P < 0.01). The allosteric activators ADP (0.1-1.0 mM) and L-leucine (1.0-10.0 mM) induce a concentration-dependent enzyme stimulation that is proportionally greater for the nerve tissue-specific GDH (up to 1,600%) than for the housekeeping enzyme (up to 150%). When used together at lower concentrations, ADP (10-50 mM) and L-leucine (75-200 microM) act synergistically in stimulating GDH activity. GTP exerts a powerful inhibitory effect (IC(50) = 0.20 mM) on the housekeeping GDH; in contrast, the nerve tissue isoenzyme is resistant to GTP inhibition. Thus, although the housekeeping GDH is regulated primarily by GTP, the nerve tissue GDH activity depends largely on available ADP or L-leucine levels. Conditions associated with enhanced hydrolysis of ATP to ADP (e.g., intense glutamatergic transmission) are likely to activate nerve tissue-specific GDH leading to an increased glutamate flux through this pathway.

Nerve tissue-specific (GLUD2) and housekeeping (GLUD1) human glutamate dehydrogenases are regulated by distinct allosteric mechanisms: implications for biologic function

Human glutamate dehydrogenase (GDH), an enzyme central to the metabolism of glutamate, is known to exist in housekeeping and nerve tissue-specific isoforms encoded by the GLUD1 and GLUD2 genes, respectively. As there is evidence that GDH function in vivo is regulated, and that regulatory mutations of human GDH are associated with metabolic abnormalities, we sought here to characterize further the functional properties of the two human isoenzymes. Each was obtained in recombinant form by expressing the corresponding cDNAs in Sf9 cells and studied with respect to its regulation by endogenous allosteric effectors, such as purine nucleotides and branched chain amino acids. Results showed that L-leucine, at 1.0 mM:, enhanced the activity of the nerve tissue-specific (GLUD2-derived) enzyme by approximately 1,600% and that of the GLUD1-derived GDH by approximately 75%. Concentrations of L-leucine similar to those present in human tissues ( approximately 0.1 mM:) had little effect on either isoenzyme. However, the presence of ADP (10-50 microM:) sensitized the two isoenzymes to L-leucine, permitting substantial enzyme activation at physiologically relevant concentrations of this amino acid. Nonactivated GLUD1 GDH was markedly inhibited by GTP (IC(50) = 0.20 microM:), whereas nonactivated GLUD2 GDH was totally insensitive to this compound (IC(50) > 5,000 microM:). In contrast, GLUD2 GDH activated by ADP and/or L-leucine was amenable to this inhibition, although at substantially higher GTP concentrations than the GLUD1 enzyme. ADP and L-leucine, acting synergistically, modified the cooperativity curves of the two isoenzymes. Kinetic studies revealed significant differences in the K:(m) values obtained for alpha-ketoglutarate and glutamate for the GLUD1- and the GLUD2-derived GDH, with the allosteric activators differentially altering these values. Hence, the activity of the two human GDH is regulated by distinct allosteric mechanisms, and these findings may have implications for the biologic functions of these isoenzymes.

Proton magnetic resonance spectroscopy in an Italian family with spinocerebellar ataxia type 1

Linkage and DNA analysis, magnetic resonance (MR) imaging, and single-voxel proton MR spectroscopy were obtained in 10 members of an Italian kindred with spinocerebellar ataxia type 1 (SCA1). The size of the basis pontis, cerebellar hemispheres, middle cerebellar peduncles, and medulla oblongata were decreased in 4 members carrying the SCA1 gene, compared with 6 unaffected subjects. Diffuse signal changes in the pons and cerebellum were observed only in the carrier with the longest disease duration and greatest disability. The N-acetylaspartate/creatine ratio and the choline/creatine ratio in the basis pontis were markedly decreased in 2 symptomatic SCA1 carriers and moderately decreased in 2 asymptomatic SCA1 carriers, compared with the unaffected family members and a control group of 10 healthy volunteers. Minor decreases in the N-acetylaspartate/creatine ratio and the normal choline/creatine ratio were observed in the cerebellar hemisphere of the SCA1 carriers. Reduction of the N-acetylaspartate/creatine ratio, demonstrated by MR spectroscopy in the pons, is likely to reflect a loss of neuronal viability and might represent a biochemical marker of SCA1 more sensitive than brainstem and cerebellum atrophy and signal changes shown by MR imaging.

Clinical aspects of hereditary ataxias

The hereditary ataxias are a group of complex genetic disorders the understanding of which is undergoing a revolution because of advances in molecular genetics. Within the last few years, at least seven different gene loci have been found to be responsible for these syndromes, and the search is on for additional loci that undoubtedly exist. This review summarizes the clinical features of the various hereditary ataxias with known gene loci, as well as others that are now defined on a clinical basis. It also deals with some of the imaging and neuropharmacologic advances that have been made in this group of disorders.

Glutamate dehydrogenase deficiency in Machado-Joseph disease

We studied the activity of glutamate dehydrogenase (GDH) in leukocytes from 23 patients with dominantly inherited ataxia. All the patients were assessed with a rating scale for ataxias and met the clinical criteria for the diagnosis of Machado-Joseph disease. The mean age of onset of symptoms was 37.8, SD 13.4 years and the duration of the disease was 7.4, SD 4.9. Leukocyte GDH activity was significantly decreased (p < 0.001) when compared to 20 normal controls. These data extend previous reports indicating that a GDH deficiency is present in peripheral tissues from some patients with spinocerebellar degenerations. Furthermore, this study suggests that a genetic deficiency of GDH may underlie some forms of dominant ataxias; this deficiency may be marked in patients with Machado-Joseph disease and is not specific for any type of multiple system atrophy.

Amyotrophic lateral sclerosis: glutamate dehydrogenase and transmitter amino acids in the spinal cord

Measurements were taken of the activity of glutamate dehydrogenase (GDH) and the levels of transmitter amino acids in anatomically dissected regions of cervical and lumbar spinal cord in eight patients dying with amyotrophic lateral sclerosis (ALS) and in 11 neurologically normal controls. GDH activity was considerably increased in lateral and ventral white matter and in the dorsal horn of the ALS cervical spinal cord, but normal in the ventral horn and the dorsal columns. Similar, although less pronounced, GDH changes were found in the lumbar enlargement. The mean concentrations of aspartate and glutamate were reduced in all regions of ALS spinal cord investigated. Taurine concentrations were significantly increased in several subdivisions of cervical spinal cord, but normal in lumbar regions. Glycine levels were significantly reduced in lumbar ventral and dorsal horns. There was no striking change in spinal cord GABA levels in our ALS patients. It is suggested that the reduced levels of glutamate and aspartate as well as the elevated GDH activity in the spinal cord of ALS patients may reflect an overactivity of the neurons releasing these potentially excitotoxic amino acids and thus may be causally related to the spinal neuro-degenerative changes characteristic of ALS.

Multiple system degeneration with glutamate dehydrogenase deficiency: pathology and biochemistry

The neuropathological findings in a patient with antemortem diagnosis of olivopontocerebellar atrophy (OPCA) and reduced leucocytic glutamate dehydrogenase (GDH) activity included cerebellar cortical degeneration, most marked in the superior vermis, mild atrophy of the pons and the inferior olivary nucleus, marked reduction of anterior horn cells at all levels and gliosis in both lateral columns. GDH activities and their thermolability in "soluble" and "particulate" fractions in the cerebral cortex, cerebellar hemisphere and vermis were not significantly different from the values in two control brains. GDH mRNA in the patient's brain was not altered in size or amount.

Leukocyte glutamate dehydrogenase and CSF amino acids in late onset ataxias

Leukocyte glutamate dehydrogenase (GDH) activity was measured in 11 healthy control subjects, 16 neurological controls, 12 patients with dominant late onset ataxia, 15 with sporadic late onset ataxia and 8 with alcoholic cerebellar ataxia. Serum hexosaminidase activity was also determined in ataxic patients. Concentrations of free amino acids were determined in the lumbal CSF of 16 neurological controls, 8 patients with late onset ataxia and 5 with alcoholic ataxia. Mean total GDH activity was reduced significantly in dominant (p less than 0.05) and sporadic (p less than 0.01) cerebellar ataxia, while the heat-labile form was decreased significantly (p less than 0.01) only in sporadic ataxia. All GDH activities were within normal range in patients with alcoholic ataxia. The serum hexosaminidase activities were also within reference range in all patient groups. The CSF concentrations of alanine, glycine, methionine and valine were significantly elevated and those of GABA and glutamate were normal in patients with late onset ataxia as compared to neurological controls. The most significant (p less than 0.01) increase was found for methionine. The amino acid levels of patients with alcoholic ataxia did not differ from those of the controls. The results suggest that GDH activity is only partially decreased in some ataxic patients and that altered amino acid metabolism may be reflected in the CSF.

Leukocyte glutamate dehydrogenase and CSF amino acids in late onset ataxias

Leukocyte glutamate dehydrogenase (GDH) activity was measured in 11 healthy control subjects, 16 neurological controls, 12 patients with dominant late onset ataxia, 15 patients with sporadic late onset ataxia and 8 with alcoholic cerebellar ataxia. Serum hexosaminidase activity was also determined in ataxic patients. Concentrations of free amino acids were determined in the lumbal CSF of 16 neurological controls, 8 patients with late onset ataxia and 5 with alcoholic ataxia. Mean total GDH activity was reduced significantly in dominant (p less than 0.05) and sporadic (p less than 0.01) cerebellar ataxia, while the heat-labile form was decreased significantly (p less than 0.01) only in sporadic ataxia. All GDH activities were within normal range in patients with alcoholic ataxia. The serum hexosaminidase activities were also within reference range in all patient groups. The CSF concentrations of alanine, glycine, methionine and valine were significantly elevated and those of GABA and glutamate were normal in patients with late onset ataxia as compared to neurological controls. The most significant (p less than 0.01) increase was found for methionine. The amino acid levels of patients with alcoholic ataxia did not differ from those of the controls. The results suggest that GDH activity is only partially decreased in some ataxic patients and that altered amino acid metabolism may be reflected in the CSF.

Neuropathology in movement disorders

This review concentrates on the definition and classification of degenerative movement disorders in which Parkinsonian symptoms are often prominent. The pathological spectrum and clinical manifestations of Lewy body disease are described, and associations with Alzheimer's disease and motor neuron disease are explored. A classification of pallidonigral degenerations is based on clinical features, distribution of pathology, and morphological abnormalities; some of these patients have mild nigral degeneration and no Parkinsonian features. Many other juvenile and familial Parkinsonian cases are not included among the pallidonigral degenerations. Most of these latter syndromes have been organised into preliminary groups, in particular, autosomal dominant dystonia-Parkinson syndrome, juvenile Parkinsonian disorder and autosomal dominant Lewy body disease.