Respiratory chain and mitochondrial deoxyribonucleic acid in blood cells from patients with focal and generalized dystonia

[Update on the etiology and pathogenesis of muscle dystonia]

Muscle dystonia is one of the most common extrapyramidal diseases and is the third most common after essential tremor and Parkinson's disease. The introduction of diagnostic methods expanded the understanding of the genetic basis of muscle dystonia and neurophysiological mechanisms of dystonic phenomena. However, the questions of the etiology and pathogenesis of dystonia still remain the subject of close interest of researchers. The review provides up-to-date information about the etiology and pathogenesis of muscle dystonia. Recent changes in the genetic nomenclature of dystonia are described. Modern ideas about the pathogenetic significance of such mechanisms as abnormalities of neural inhibition, disturbances of sensorimotor integration, and abnormalities of neural plasticity are considered. Recent research data support the concept of systemic sensorimotor disintegration, including not only basal ganglia dysfunction, but also motor network disorders involving the cerebellum, cortex, midbrain, thalamus and other areas.

Kearns-Sayre syndrome "plus". Classical clinical findings and dystonia

We present a boy of eight years of age with symptoms of Kearns-Sayre syndrome (KSS) characterised by ophthalmoparesis, palpebral ptosis, mitochondrial myopathy, pigmentous retinitis, associated to short stature, cerebellar signs, cardiac blockade, diabetes mellitus, elevated cerebrospinal fluid protein concentration, and focal hand and foot dystonia. The skeletal muscle biopsy demonstrated ragged red fibers, cytochrome C oxidase-negative and succinate dehydrogenase-positive fibers. The magnetic resonance imaging showed symmetrical signal alteration in tegmentum of brain stem, pallidum and thalamus. Mitochondrial DNA analysis from skeletal muscle showed a deletion in heteroplasmic condition. The association of dystonia to KSS, confirmed by molecular analysis, is first described in this case, and the importance of oxidative phosphorylation defects in the physiopathogenesis of this type of movement disorder is stressed.

1H magnetic resonance spectroscopy of the lentiform nucleus in primary focal hand dystonia

Several radiologic findings point toward the lentiform nucleus as a possible site of lesion in primary dystonia. Histologic examinations, however, have shown inconsistent results. 1H-magnetic resonance spectroscopy (MRS) has proved helpful to assess neuronal degeneration in a variety of basal ganglia disorders. MRS data of dystonia patients are, however, lacking so far. 1H-MRS centered on the lentiform nuclei was performed in 14 patients with primary focal hand dystonia and in 12 healthy control subjects using a 1.5-T MR imager. No statistically significant differences of N-acetylaspartate/creatine and lactate/creatine ratios were found between patients and control subjects. Based on these data, the authors found no evidence that primary focal dystonia was associated with a conspicuous loss of lentiform nucleus neurons or a marked disturbance of the aerobic metabolism, although minor abnormalities cannot be excluded because of the possibly limited sensitivity of the method.

Dystonia

Many different disorders have dystonia as the only or primary sign. The list of causes for dystonia increases yearly and now includes three mapped loci for primary torsion dystonia, although other susceptibility genes are suspected. Study of one of these primary torsion dystonia loci (DYT1) has culminated in the cloning of a gene which codes for a novel protein, torsin A. Physiological and positron emission tomography analyses suggest that dystonia results from impaired inhibition at cortical and subcortical levels; these physiological changes may in turn be due to striatal dysfunction and a mismatch or imbalance between the direct and indirect pathways. Future study of normal and mutant torsin A, as well as the identification of other primary torsion dystonia genes, should help elucidate the mechanisms underlying dystonia.

Human complex I defects in neurodegenerative diseases

Complex I deficiency, either specific or associated with other respiratory chain defects, has been identified in myopathies, encephalomyopathies and in three 'neurodegenerative' disorders: Parkinson's disease, dystonia and Leber's hereditary optic neuropathy. The complex I defect is expressed in blood in all these three but, to date, only in LHON have specific mitochondrial DNA mutations been identified. Recent work with rho degrees cybrids indicates that, in a subgroup of patients at least, the complex I deficiency is determined by mtDNA, in contrast to dystonia where a nuclear gene defect or toxic influence appears a more likely cause. The actions of specific toxins, e.g., MPTP continue to play an important role in our understanding of pathogenesis of neurodegeneration, particularly in PD.

Complex I function in familial and sporadic dystonia

A significant proportion of patients with inborn errors of the mitochondrial respiratory chain exhibit movement disorders, particularly dystonia. Point mutations of mitochondrial DNA (mtDNA) are usually expressed systemically, and defects of platelet respiratory chain function have been described in patients with mtDNA mutations and Leber's hereditary optic neuropathy (LHON). Recent reports have documented families with dystonia in association with LHON and mtDNA complex I gene mutations. We have examined mitochondrial function in platelet mitochondria from patients with familial generalized dystonia (linked or not linked to 9q34) and sporadic focal dystonia. We confirm a previous report of a specific complex I defect in patients with sporadic focal dystonia but could not find any abnormality in patients with familial generalized dystonia, linked or not to 9q34. These results support the existence of a mitochondrial deficiency in sporadic focal dystonia and provide a biochemical dimension to the clinical and genetic distinction between focal and generalized familial dystonia.

Inhibition of brain macrophage/microglial respiratory chain enzyme activity in experimental autoimmune encephalomyelitis of the Lewis rat

We measured the activities of five respiratory chain enzymes in brain macrophages/microglial cells from Lewis rats with experimental autoimmune encephalomyelitis (EAE) and found a significant reduction of the activity of nicotinamide adenine dinucleotide-dehydrogenase (NADH-DH), succinate cytochrome c reductase (SCCR) and succinate dehydrogenase (SDH) when compared with age-matched healthy control animals. The inhibition of NADH-DH (complex I) was specific for EAE, while we also found a reduction of SCCR and SDH activities (complex II) in newborn rats and adjuvant-immunised rats. Activities of NADH cytochrome c reductase (NCCR) and cytochrome c oxidase (COX) were not significantly changed. These observations demonstrate an impairment of brain macrophage/microglial respiratory chain function in central nervous system inflammation.