RESUMEN
BACKGROUND: MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) is one of the more common mitochondrial encephalomyopathies. About 80% of MELAS cases are caused by transition 3243A-->G in the mitochondrial tRNA(Leu(UUR)) gene (MT-TL1). Other mutations in MT-TL1, other mitochondrial tRNA genes and mitochondrial-encoded subunits of respiratory complex I account for the remainder of cases. OBJECTIVE: To characterise the molecular basis of a MELAS case without a mutation in any recognised MELAS target gene. RESULTS AND METHODS: Deletion of a single nucleotide (7630delT) within MT-CO2, the gene of subunit II of cytochrome c oxidase (COX), was identified by mitochondrial DNA (mtDNA) sequencing. The deletion-induced frameshift results in a stop codon close to the 5' end of the reading frame. The lack of subunit II (COII) precludes the assembly of COX and leads to the degradation of unassembled subunits, even those not directly affected by the mutation. Despite mitochondrial proliferation and transcriptional upregulation of nuclear and mtDNA-encoded COX genes (including MT-CO2), a severe COX deficiency was found with all investigations of the muscle biopsy (histochemistry, biochemistry, immunoblotting). CONCLUSIONS: The 7630delT mutation in MT-CO2 leads to a lack of COII with subsequent misassembly and degradation of respiratory complex IV despite transcriptional upregulation of its subunits. The causal association of the resulting isolated COX deficiency with MELAS is at odds with current concepts of the biochemical deficits underlying this common mitochondrial disease, and indicates that the genetic and pathobiochemical heterogeneity of MELAS is greater than previously appreciated.
Asunto(s)
Deficiencia de Citocromo-c Oxidasa/enzimología , Deficiencia de Citocromo-c Oxidasa/genética , Complejo IV de Transporte de Electrones/genética , Síndrome MELAS/enzimología , Síndrome MELAS/genética , Adulto , Secuencia de Aminoácidos , Secuencia de Bases , Deficiencia de Citocromo-c Oxidasa/complicaciones , ADN Mitocondrial/genética , Humanos , Síndrome MELAS/etiología , Síndrome MELAS/patología , Masculino , Datos de Secuencia Molecular , Músculos/enzimología , ARN Mensajero/genética , ARN Mensajero/metabolismo , Eliminación de SecuenciaRESUMEN
The Vienna Transdanube Aging (VITA) study searches for early markers of Alzheimer's disease (AD) by examining the mental status in a community-based cohort of 606, 75-years old volunteers that are then related to various clinical and genetic analyses. To determine whether mutations in mtDNA are involved in expression of AD, the mtDNA of 79 "control" participants is screened for alterations by sequencing of "hot-spot-regions". This study on mtDNA mutations has eliminated the influence of aging on the occurrence of mtDNA alterations by sequencing samples from persons at the age of exactly 75 years. Thus, our cohort reveals a snap-shot of mitochondrial sequences of elderly persons. So far, a high percentage (56%) of persons with known or unknown mutations in the fragments analyzed were found. These data will be compared in due time to a cohort of participants with proven late-onset AD.
Asunto(s)
Enfermedad de Alzheimer/genética , ADN Mitocondrial/genética , Predisposición Genética a la Enfermedad/genética , Anciano , Enfermedad de Alzheimer/epidemiología , Sustitución de Aminoácidos/genética , Austria/epidemiología , Estudios de Cohortes , Estudios Transversales , Análisis Mutacional de ADN , Femenino , Pruebas Genéticas , Genotipo , Haplotipos/genética , Humanos , Estudios Longitudinales , Masculino , Mutación/genética , Polimorfismo de Nucleótido Simple/genética , Valor Predictivo de las Pruebas , RiesgoRESUMEN
The SJL mouse strain has been widely used as an animal model for experimental autoimmune encephalitis (EAE), inflammatory muscle disease and lymphomas and has also been used as a background strain for the generation of animal models for a variety of diseases including motor neurone disease, multiple sclerosis and atherosclerosis. Recently the SJL mouse was shown to have myopathy due to dysferlin deficiency, so that it can now be considered a natural animal model for limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM). We have cloned the mouse dysferlin cDNA and analysis of the sequence shows that the mouse dysferlin gene is characterized by six C2 domain sequences and a C-terminal anchoring domain, with the human and the mouse dysferlin genes sharing > 90% sequence homology overall. Genomic analysis of the SJL mutation confirms that the 171 bp RNA deletion has arisen by exon skipping resulting from a splice site mutation. The identification of this mutation has implications for the various groups using this widely available mouse stock.
Asunto(s)
Eliminación de Gen , Proteínas de la Membrana , Proteínas Musculares/genética , Distrofia Muscular Animal/genética , Secuencia de Aminoácidos , Animales , Clonación Molecular , Modelos Animales de Enfermedad , Disferlina , Ratones , Ratones Endogámicos C57BL , Ratones Mutantes , Datos de Secuencia Molecular , Distrofias Musculares/genética , FenotipoRESUMEN
In the muscle biopsy of a female patient with chronic progressive external ophthalmoplegia (CPEO), myopathy, and exercise intolerance, the heteroplasmic deletion of a single nucleotide (DeltaT5885) in the mitochondrial tRNA tyrosine gene (tRNA(Tyr)) was found. The mutation was associated with the mitochondrial phenotype of individual muscle fibers, suggesting a causal association of DeltaT5885 with the mitochondrial disease phenotype. The microdeletion was absent from the patient's and her relatives' blood, indicating a spontaneous somatic origin.