Mitochondrial disease heterogeneity: a prognostic challenge.

Mitochondrial diseases are a heterogeneous group of progressive, genetically transmitted, multisystem disorders caused by impaired mitochondrial function. The disease course for individuals with mitochondrial myopathies varies greatly from patient to patient because disease progression largely depends on the type of disease and on the degree of involvement of various organs which makes the prognosis unpredictable both within the same family and among families with the same mutation. This is particularly, but not exclusively, true for mitochondrial disorders caused by mtDNA point mutations, which are maternally inherited and subject to the randomness of the heteroplasmy. For this reason, the prognosis cannot be given by single mitochondrial disease, but should be formulated by any single mitochondrial disease-related event or complication keeping in mind that early recognition and treatment of symptoms are crucial for the prognosis. The following approach can help prevent severe organ dysfunctions or at least allow early diagnosis and treatment of disease-related complications.

Mitochondrial respiratory chain dysfunction in muscle from patients with amyotrophic lateral sclerosis.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a major cause of neurological disability and its pathogenesis remains elusive despite a multitude of studies. Although defects of the mitochondrial respiratory chain have been described in several ALS patients, their pathogenic significance is unclear. OBJECTIVE: To review systematically the muscle biopsy specimens from patients with typical sporadic ALS to search for possible mitochondrial oxidative impairment. DESIGN: Retrospective histochemical, biochemical, and molecular studies of muscle specimens. SETTING: Tertiary care university. Subjects Fifty patients with typical sporadic ALS (mean age, 55 years). Main Outcome Measure Number of patients showing a clear muscle mitochondrial dysfunction assessed through histochemical and biochemical muscle analysis. RESULTS: Histochemical data showed cytochrome c oxidase (COX)-negative fibers in 46% patients. Based on COX histochemical activity, patients fell into 4 groups: 27 had normal COX activity; and 8 had mild (2-4 COX-negative fibers of 100 fibers), 8 had moderate (5-10 COX-negative fibers of 100), and 7 had severe (>10 COX-negative fibers of 100) COX deficiency. Spectrophotometric measurement of respiratory chain activities showed that 3 patients with severe histochemical COX deficiency also showed combined enzyme defects. In 1 patient, COX deficiency worsened in a second biopsy taken 9 months after the first. Among the patients with severe COX deficiency, one had a new mutation in the SOD1 gene, another a mutation in the TARDBP gene, and a third patient with biochemically confirmed COX deficiency had multiple mitochondrial DNA deletions detectable by Southern blot analysis. CONCLUSIONS: Our data confirm that the histochemical finding of COX-negative fibers is common in skeletal muscle from patients with sporadic ALS. We did not find a correlation between severity of the oxidative defect and age of the patients or duration of the disease. However, the only patient who underwent a second muscle biopsy did show a correlation between severity of symptoms and worsening of the respiratory chain defect. In 7 patients, the oxidative defect was severe enough to support the hypothesis that mitochondrial dysfunction must play a role in the pathogenesis of the disease.

Hepatocerebral form of mitochondrial DNA depletion syndrome: novel MPV17 mutations.

BACKGROUND: Autosomal recessive mutations in MPV17 (OMIM *137960) have been identified in the hepatocerebral form of mitochondrial DNA depletion syndrome (MDS). OBJECTIVE: To describe the clinical, morphologic, and genetic findings in 3 children with MPV17-related MDS from 2 unrelated families. DESIGN: Case report. SETTING: Academic research. MAIN OUTCOME MEASURES: We identified 3 novel pathogenic mutations in 3 children. RESULTS: Two children were homozygous for nonsense mutation p.W120X. A third child was compound heterozygous for missense mutation p.G24W and for a macrodeletion spanning MPV17 exon 8. All patients demonstrated lactic acidosis, hypoglycemia, hepatomegaly, and progressive liver failure. Neurologic symptoms manifested at a later stage of the disease. Death occurred within the first year of life in all 3 patients. CONCLUSIONS: These data confirm that MPV17 mutations are associated with a 2-stage syndrome. The first symptoms are metabolic and rapidly progress to hepatic failure. This stage is followed by neurologic involvement affecting the central and peripheral systems.

Effect of ezetimibe and/or simvastatin on coenzyme Q10 levels in plasma: a randomised trial.

BACKGROUND: HMG-CoA reductase inhibitors ('statins') have been associated with a decrease in ubidecarenone (ubiquinone) levels, a lipophilic enzyme also known as coenzyme Q10 (CoQ10), due to inhibition of mevalonate synthesis. There is speculation that a decrease in CoQ10 levels may be associated with statin-induced myopathy. The cholesterol absorption inhibitor ezetimibe increases endogenous cholesterol synthesis. The purpose of this study was to examine (i) the effects of ezetimibe and simvastatin on plasma CoQ10 levels and (ii) whether ezetimibe coadministered with simvastatin abrogates the suggested statin-induced decrease in the CoQ10 plasma levels. METHODS: Seventy-two healthy male subjects were enrolled in a single-centre, randomised, parallel-group study with three arms. Subjects received ezetimibe 10 mg/day, simvastatin 40 mg/day or the combination of ezetimibe 10 mg/day plus simvastatin 40 mg/day for 14 days. RESULTS: Baseline CoQ10 (0.99 +/- 0.30 mg/L) levels for the combined groups remained unchanged in the ezetimibe group (0.95 +/- 0.24 mg/L), and significantly decreased in the simvastatin and combination groups (0.82 +/- 0.18 mg/L, p = 0.0002 and 0.7 +/- 0.22 mg/L, p < 0.0001, respectively). There was a correlation between the percentage change in the levels of low-density lipoprotein-cholesterol (LDL-C) and the percentage change in CoQ10 levels in all treatment groups (correlation coefficient [R] = 0.67, p < 0.0001). The ratios of CoQ10 levels to LDL-C levels were significantly increased in all treatment groups (p < 0.0001). CoQ10 level was independent of cholesterol synthesis or absorption markers. CONCLUSIONS: Simvastatin and the combination of simvastatin and ezetimibe significantly decrease plasma CoQ10 levels whereas ezetimibe monotherapy does not. There is a significant correlation between the CoQ10 level decrease and the decrease in total and LDL-C levels in all three treatment groups, suggesting that the CoQ10 decrease may reflect the decrease in the levels of its lipoprotein carriers and might not be statin-specific. The statin-associated CoQ10 reduction is not abrogated through ezetimibe coadministration. Changes of CoQ10 levels are independent of cholesterol synthesis and absorption.

Hereditary ferritinopathy: a novel mutation, its cellular pathology, and pathogenetic insights.

We report a family of French Canadian and Dutch ancestry with hereditary ferritinopathy (neuroferritinopathy) and a novel mutation (C insertion at nt646-647 in exon 4) in the ferritin light chain gene, resulting in a longer than normal protein. Our failure to immunostain most of the abnormal ferritin deposits in the proband with a conformation-dependent monoclonal antibody to ferritin light chain supported a previously postulated conformational change of ferritin light chain in this disease. The posterior putamen and cerebellum were the primary pathologic loci in our proband, but asymptomatic hepatocytic intranuclear accumulations of iron and ferritin also were present. Both neurons and glia displayed highly distinctive, if not pathognomonic, swollen to vacuolated nuclei containing ferritin and iron. Hyaline deposits, again staining for both ferritin and iron, were additional morphologic features that may be unique to the ferritinopathies. The iron, at least in putamen where there was a nearly 40-fold increase, appeared to be both in the ferrous (Fe2+) and ferric (Fe3+) form; it was the most likely cause of the observed neuronal and glial apoptosis. We found morphologic evidence of both lipid peroxidation and abnormal nitration of proteins in putaminal neurons and glia, confirming the expected oxidative stress due to this excessive iron. Biochemical and immunohistochemical abnormalities in mitochondria also were demonstrated, probably due to an imbalance in iron homeostasis that had a deleterious effect on the respiratory chain.

Miopatia por deficiência de succinato citocromo-c redutase: possível defeito no complexo 11 da cadeia respiratória / Myopathy due to succinate cytochrome-c reductase deficiency: possible deficiency in the complex 11 of the respiratory chain

Relato do caso de mulher de 24 anos de idade que apresentava astenia desde a puberdade, com agravamenteo nos últimos anos, cuja biópsia muscular revelou grande acúmulo de mitocôndrias. As dosagens dos enzimas mitocondriais mostrou importante reduçäo da succinato-citocromo-C-redutase, sugerindo defeito na cadeia respiratória a nível do complexo II. Medicada com altas doses de vitamina C e K, melhorou da força muscular. Säo feitas consideraçöes a respeito das principais síndromes com miopatias mitocondriais, bem como a respeito dos métodos de investigaçäo em defeitos da cadeia respiratória

Deficiência muscular de carnitina: relato de 8 casos com estudo clínico, eletromiográfico, histoquímico e bioquímico muscular / Muscle carnitive defeciency: report of 8 cases with clinical eletromyographic, histochemical biochemical study

Säo relatados os casos de 8 pacientes, sendo 7 do sexo masculino, cuja idade variou entre 5 dias e 64 anos. Sete pacientes apresentavam diminuçäo da força muscular e todos apresentavam, nas biópsias musculares, acúmulo de lipídios. Os síntomas iniciaram nos primeiros dias de vida em três pacientes, na infância em dois, na idade adulta em dois; um dos casos apresentava-se assintomático aos 64 anos de idade (heterozigoto?). Em graus variáveis os pacientes apresentavam dificuldades na deglutiçäo, atrofia muscular, dificuldades na mastigaçäo, parestesias em membros inferiores, hepatomegalia e esplenomegalia. Cinco casos tinham história familiar e um relatava recorrências dos sintomas. Todos apresentavam aumento dos enzimas séricos, principalmente da creatinoquinase. A eletromiografia foi compatível a envolvimento muscular primário em um caso, desenervaçäo em dois neuromiopático em dois, näo tendo sído realizada em três casos. Na biópsia muscular, em todos os casos, além do acúmulo de lipídios, ocorriam: componente de desenervaçäo em 4, miopatia crônica em 4, atrofia de fibras do tipo II em um. Em dois casos, as alteraçöes histológicas eram sugestivas de atrofia espinhal infantil. Um dos casos, possivelmente pertencente à forma sistêmica de deficiência de carnitina, possuia importante envolvimento miocárdio, vindo a falecer. Säo discutidos aspectos clínicos, metabólicos e terapêuticos da deficiências musculares de carnitina