Leukocyte glutamate dehydrogenase and CSF amino acids in late onset ataxias

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.

Neurometabolic effects of ACTH on free amino compounds in opsoclonus-myoclonus syndrome

To evaluate the possible role of central free amino compounds in pediatric opsoclonus-myoclonus syndrome (OMS), 21 cerebrospinal fluid (CSF) amino compounds were measured by an amino acid analyzer or mass spectroscopy in 74 anesthetized children, 54 with OMS and 20 age-matched neurological controls. In OMS, only phosphoethanolamine was increased compared to controls; OMS severity and duration had significant converse effects on alanine and phosphoethanolamine. In contrast, corticotropin (ACTH) treatment was associated with increased alanine and phenylalanine, and decreased taurine compared to controls and untreated OMS, and increased glutamine, lysine, ornithine, and tyrosine compared to untreated OMS. Other than low taurine, these effects were not found with corticosteroid treatment, and non-steroidogenic immunotherapy had no effect. The ACTH dose-association was most apparent for alanine and phosphoethanolamine, but lysine and ornithine were also higher in the high-dose ACTH group. There were no significant disease- or treatment-associated perturbations in GABA, glycine, or other amino acids. These data suggest a unique pattern of ACTH effects on non-neurotransmitter CSF amino compounds, for the most part not shared by steroids.

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.

Brain amino acid reductions in one family with chromosome 6p-linked dominantly inherited olivopontocerebellar atrophy

We measured the levels of aspartate, glutamate, gamma-aminobutyric acid (GABA), and other amino acids in autopsied brain of 6 patients from one family (Pedigree S) with dominantly inherited olivopontocerebellar atrophy. A previous demonstration of reduced aspartate concentration in plasma of affected members of this family suggested the possibility of a generalized disorder of amino acid metabolism affecting the brain. As compared with the control levels, mean levels of aspartate and glutamate were markedly reduced by about 70 and 40%, respectively, in the degenerated cerebellar cortex from the patients. Since the cerebellar aspartate reduction likely exceeds the amount that could be explained by neuronal loss, other factors such as abnormal aspartate metabolism, neurotransmitter turnover, or both are probably involved. Mean aspartate, glutamate, and GABA levels were also reduced by about 10 to 30% in most of the 16 examined extracerebellar brain areas in which no or, at most, mild neuronal cell loss was observed by semiquantitative estimation. Concentrations of taurine, glutamine, and omicron-phosphoethanolamine were normal in all brain areas examined. Our biochemical data provide support to the presence of a generalized, but quantitatively mild, disturbance in amino acid metabolism in patients with olivopontocerebellar atrophy from Pedigree S. The regionally widespread amino acid reductions in the brain, of as yet unknown pathophysiological significance, could be due to a failure of one or more enzymes involved in aspartate and glutamate metabolism.

A significant reduction of putative transmitter amino acids in cerebrospinal fluid of patients with Parkinson's disease and spinocerebellar degeneration

We evaluated the concentrations of the putative transmitter amino acids in the cerebrospinal fluid, and found a significant reduction of glutamate, aspartate, gamma-aminobutyric acid (GABA), and glycine concentrations in parkinsonian patients. There was no difference in amino acid concentrations between parkinsonian patients receiving L-DOPA and those not receiving L-DOPA. A similar decrease of glutamate and aspartate concentrations was found in patients with spinocerebellar degeneration. Concentrations of asparagine, glycine and taurine were also significantly decreased in patients with late cortical cerebellar atrophy.