Michelle Coquet

Mitochondrial myopathy studies on permeabilized muscle fibers

ABSTRACT: Respiratory parameters of skeletal muscle were determined in permeabilized muscle fibers by adapting a technique described by Veksler et al. for cardiac fibers (Biochim Biophys Acta, 892:191–196, 1987). This method consists of the permeabilization of muscle fibers by saponin by allowing respiratory substrates and inhibitors to reach the mitochondria. In this way, the mitochondria may be studied inside the fibers as if they were isolated. We have verified, using various techniques, that the mitochondria remain intact during this procedure. This method has been applied to the study of six newborn infants for whom a diagnosis of a mitochondrial defect was suspected. In all cases, the defect was to be found on the permeabilized fibers, and this was confirmed by an enzymatic study. The advantage of this new method, associated with the measurement of the enzymatic activities on a crude homogenate, is to enable a simple and rapid diagnosis on a small amount of sample without damaging the mitochondria during the isolation procedure.

Fatal neonatal liver failure and mitochondrial cytopathy: An observation with antenatal ascites

Mitochondrial cytopathies are multisystemic diseases of extremely variable expression caused by a deficiency in oxidative phosphorylation. Only five cases of neonatal liver failure in the context of mitochondrial cytopathy have been reported, with incomplete morphological data of the liver in three. In the case presented here, ascites had been diagnosed prenatally and liver failure was particularly severe (factor V less than 15% with fatal coma the fourth day). Histologically there were incomplete cirrhosis, microvesicular steatosis, major canalicular cholestasis with proliferative neocholangioles, and bile duct thrombi. There were also some iron pigments in the periportal area and partial glycogen depletion. By electron microscopy, mitochondria in numerous hepatocytes appeared abnormal with occasional cristae in a fluffy matrix, some containing dense inclusions. Study of respiratory chain activity showed a defect in cytochrome c oxidase (complex IV), revealed by oxygraphic measurement on fresh muscle biopsy and confirmed by spectrophotometric enzymatic assays performed on muscle and liver homogenates. The association of neonatal liver failure with hyperlactacidemia warrants investigation into a deficiency in oxidative phosphorylation.

Menkes disease: study of the mitochondrial respiratory chain in three cases

Mitochondrial oxidative metabolism in three patients with typical Menkes disease was studied. In two cases, a general decrease in all of the respiratory chain complex activities (I, II, III and IV) was observed. However, in the most severe case, these activities were entirely normal. Our results emphasize the diversity of the cellular expression of Menkes disease which can, in some cases, be associated with a mitochondrial encephalomyopathy.

Partial Triplication of mtDNA in Maternally Transmitted Diabetes Mellitus and Deafness

We thank J. P. Mazat for his helpful discussion, M. Perrot for the DNA quantification, and C. Mehaye for technical assistance. This work was supported by a grant from the Ministere des Affaires Sociales de la Sante et de la Ville, Projet Hospitalier de Recherche Clinique, in 1994.

Statistical Analysis of Mitochondrial Pathologies in Childhood: Identification of Deficiencies using Principal Component Analysis

Mitochondrial pathologies are a heterogeneous group of metabolic disorders that are frequently characterized by anomalies of oxidative phosphorylation, especially in the respiratory chain. The identification of these anomalies may involve many investigations, and biochemistry is a main tool. However, considering the whole set of biochemical data, the interpretation of the results by the traditionally used statistical methods remains complex and does not always lead to an unequivocal conclusion about the presence or absence of a respiratory chain defect. This arises from three main problems: (a) the absence of an a priori-defined control population, because the determination of the control values are derived from the whole set of investigated patients, (b) the small size of the population studied, (c) the large number of variables collected, each of which creates a wide variability. To cope with these problems, the principal component analysis (PCA) has been applied to the biochemical data obtained from 35 muscle biopsies of children suspected of having a mitochondrial disease. This analysis makes it possible for each respiratory chain complex to distinguish between different subsets within the whole population (normal, deficient, and, in between, borderline subgroups of patients) and to detect the most discriminating variables. PCA of the data of all complexes together showed that mitochondrial diseases in this population were mainly caused by multiple deficits in respiratory chain complexes. This analysis allows the definition of a new subgroup of newborns, which have high respiratory chain complex activity values. Our results show that the PCA method, which simultaneously takes into account all of the concerned variables, allows the separation of patients into subgroups, which may help clinicians make their diagnoses.

Coexistence d’une dermatomyosite et d’une myofasciite à macrophages

Resume Introduction Myopathie inflammatoire caracterisee par des douleurs arthro-musculaires et une asthenie chronique, avec une infiltration de l’epimysium, du perimysium et de l’endomysium peri-fasciculaires par des cellules de la lignee macrophagique, la myofasciite a macrophages est souvent associee a d’autres affections le plus souvent de nature auto-immune. Mais la coexistence avec une autre myopathie inflammatoire est relativement rare. Observation Il s’agit d’une femme de 29 ans atteinte de 2 myopathies inflammatoires distinctes, une myofasciite a macrophages et une dermatomyosite, laquelle est survenue quelques annees apres la premiere. Commentaires Dans les rares cas ou 2 myopathies inflammatoires sont associees, les liens exacts existant entre elles sont inconnus; une susceptibilite individuelle a developper des maladies musculaires est suggeree.

Muscle magnetic resonance imaging abnormalities in X-linked myopathy with excessive autophagy.

Introduction: X‐linked myopathy with excessive autophagy (XMEA) is an X‐linked recessive myopathy due to recently reported mutations in the VMA21 gene. Methods: Four men from 2 separate families were studied. The clinical presentation, genetic data, muscle biopsy, and muscle MRI were analyzed. Results: A known VMA21 mutation, c.163+4A>G, and a new mutation, c.163+3A>G, respectively, were found in the 2 families. The clinical course was characterized by onset in childhood and progressive muscle weakness with a limb‐girdle pattern. Muscle biopsy revealed a mild myopathy with an increased number of giant autophagic vacuoles. Whole‐body muscle MRI showed that pelvic girdle and proximal thighs were the most and earliest affected territories, with sparing of rectus femoris muscles. Muscle changes essentially consisted of degenerative fatty replacement. Conclusions: This study highlights a distinctive MRI pattern of muscle involvement, which can be helpful for diagnosis of XMEA, even before muscle biopsy or genetic analysis. Muscle Nerve 52: 673–680, 2015