Yolanda Campos

Molecular heterogeneity of myophosphorylase deficiency (McArdle's disease): a genotype-phenotype correlation study.

We report on 54 Spanish patients with McArdles disease from 40 unrelated families. Molecular analysis revealed that the most common R49X mutation was present in 70% of patients and 55% of alleles. The G204S mutation was less frequent and found in 14.8% of patients and 9% of mutant alleles. The W797R mutation was observed in 16.5% of patients, accounting for 13.7% of mutant alleles. Moreover, 78% of mutant alleles among Spanish patients can be identified by using polymerase chain reaction‐restriction fragment length polymorphism analysis for the R49X, G204S, and W797R mutations, which makes noninvasive diagnosis possible through molecular genetic analysis of blood DNA. Six novel mutations were found. Three were missense mutations, E348K, R601W, and A703V; two nonsense mutations, E124X and Q754X; and one single base pair deletion, 533 delA. No clear genotype‐phenotype correlation emerges from our study. Most of the mutations of uncharged and solvent inaccessible residues and the truncations must disrupt the basic structure of the protein. The mutations of charged residues would be expected to interfere with internal hydrogen bonding networks, introducing severe incompatible partnering that is caused by poor packing or electrostatic repulsions.

Renal pathology in children with mitochondrial diseases

We studied renal involvement in 42 children with mitochondrial diseases (MDs). The diagnosis of MD was established by morphological, biochemical, and molecular genetic criteria. Renal disease was considered when patients had renal failure, nephrotic syndrome, Fanconi’s syndrome or any symptomatic renal alteration. Mild tubular disorder was established if they had abnormal laboratory findings with no apparent clinical symptom. Renal involvement was found in 21 children (50%), of whom 8 had an apparent clinical picture and 13 a mild tubular disorder. Five patients with renal disease showed Debré–Toni–Fanconi’s syndrome, 2 of them with decreased glomerular filtration rate (GFR). One case had nephrotic syndrome, another one presented decreased GFR, and the last one had a neurogenic bladder and bilateral hydronephrosis. Patients with mild renal disease showed tubular dysfunction with normal GFR. Renal involvement is frequent and present in about half of the children with MD. Thus, studies for evaluating kidney function should be performed on children with MD. Conversely, patients with tubulopathy of unknown origin or progressive renal disease should be investigated for the existence of MD, especially if associated with involvement of other organs or tissues. Southern blot analysis to search for large-scale mitochondrial DNA (mtDNA) rearrangements should be performed for patients with MD and kidney involvement.

Leigh syndrome associated with the T9176C mutation in the ATPase 6 gene of mitochondrial DNA

A child with clinical and neuroradiologic evidence of Leigh syndrome (LS) had the T-to-C transition at nt 9176 in the ATPase 6 gene of mtDNA. The mutation was homoplasmic in muscle and maternally inherited. The probands mother had ataxia and harbored 93% of mutant genomes in blood, whereas three clinically unaffected maternal relatives had varying degrees of heteroplasmy in blood. These data confirm the association of the T9176C mutation with LS and extend the clinical heterogeneity of mutations in the ATPase 6 gene.

Mitochondrial DNA Haplogroups Do Not Play a Role in the Variable Phenotypic Presentation of the A3243G Mutation

Thirty-five mitochondrial (mt) DNAs from Spain that harbor the mutation A3243G in association with either MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes) syndrome or a wide array of disease phenotypes (ranging from diabetes and deafness to a mixture of chronic progressive external ophthalmoplegic symptoms and strokelike episodes) were studied by use of high-resolution restriction fragment length polymorphism analysis and control-region sequencing. A total of 34 different haplotypes were found, indicating that all instances of the A3243G mutation are probably due to independent mutational events. Haplotypes were distributed into 13 haplogroups whose frequencies were close to those of the general Spanish population. Moreover, there was no statistically significant difference in haplogroup distribution between patients with MELAS and those with disease phenotypes other than MELAS. Overall, these data indicate that the A3243G mutation harbors all the evolutionary features expected from a severely deleterious mtDNA mutation under strong negative selection, and they reveal that European mtDNA backgrounds do not play a substantial role in modulating the mutations phenotypic expression.

Biological roles of L-carnitine in perinatal metabolism

Carnitine performs a crucial role in the energy supply of tissues during fetal life and in the neonatal period by controlling the influx of fatty acids into mitochondria. Carnitine also facilitates the oxidation of pyruvate and branched chain amino acids, and contributes to the protection of cells from the deleterious actions of acyl CoAs. Carnitine further acts as a secondary antioxidant, favouring fatty acid replacement within previously oxidatively damaged membrane phospholipids. Availability of L-carnitine is essential in the developing fetus for processes underlying fetal maturation. L-carnitine is also essential for development of hepatic ketone synthesis, a central pathway for neonatal energy metabolism. Ketone bodies inhibit the oxidation of both glucose and lactate, sparing these metabolic substrates for biosynthetic functions.

Single large-scale mitochondrial DNA deletion in a patient with mitochondrial myopathy associated with multiple symmetric lipomatosis

In a nonalcoholic woman with multiple symmetric lipomatosis (MSL), muscle histochemistry showed ragged-red fibers and cytochrome c oxidase negative fibers. Southern blot analysis revealed a single deletion of mitochondrial DNA (mtDNA). We suggest that MSL is an uncommon manifestation of the wide clinical spectrum of mitochondrial disorders, in particular of those associated with single mtDNA deletions. NEUROLOGY 1996;47: 1012-1014

Exercise training in mitochondrial myopathy: a randomized controlled trial.

Patients with mitochondrial myopathies (MM) usually suffer from exercise intolerance due to their impaired oxidative capacity and physical deconditioning. We evaluated the effects of a 12‐week supervised randomized rehabilitation program involving endurance training in patients with MM. Twenty MM patients were assigned to a training or control group. For three nonconsecutive days each week, patients combined cycle exercise at 70% of their peak work rate with three upper‐body weight‐lifting exercises performed at 50% of maximum capacity. Training increased maximal oxygen uptake (28.5%), work output (15.5%), and minute ventilation (40%), endurance performance (62%), walking distance in shuttle walking test (+95 m), and peripheral muscle strength (32%–62%), and improved Nottingham Health Profile scores (21.47%) and clinical symptoms. Control MM patients did not change from baseline. Results show that our exercise program is an adequate training strategy for patients with mitochondrial myopathy. Muscle Nerve, 2005

A double mutation (A8296G and G8363A) in the mitochondrial DNA tRNALys gene associated with myoclonus epilepsy with ragged-red fibers

Objective: To define potential pathogenic mitochondrial DNA (mtDNA) point mutations in a patient with myoclonus epilepsy with ragged-red fibers (MERRF) syndrome. Background: MERRF syndrome is typically associated with point mutations in the mtDNA tRNALys gene. Methods: We performed morphologic, biochemical, and genetic analysis of muscle samples from the patient and four relatives. Molecular genetic studies included sequencing, PCR, and restriction enzyme analysis on whole muscle, blood, and single muscle fibers. Results: Muscle biopsy showed cytochrome c oxidase (COX), negative ragged-red fibers (RRF), and a defect of complex I of the mitochondrial respiratory chain. We found an A8296G transition and a G8363A mutation in the mtDNA tRNALys gene. The A8296G was almost homoplasmic in muscle and blood from the propositus and his oligosymptomatic maternal relatives. The G8363A mutation was heteroplasmic and more abundant in muscle than in blood, and its proportion correlated with clinical severity. Single muscle fiber analysis showed significantly higher levels of G8363A genomes in COX-negative than in normal fibers, and almost homoplasmic levels of mutant A8296G mtDNA in both COX-negative and normal fibers. The two mutations affect highly conserved nucleotides and were not found in controls. Conclusions: The G8363A mutation is pathogenic; the co-ocurrence of the A8296G mutation is of unclear significance and is likely to be a rare polymorphism.

Mitochondrial dysfunction associated with a mutation in the Notch3 gene in a CADASIL family

Background: Cerebral autosomal arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is characterized by recurrent subcortical ischemic strokes and dementia caused by mutations in the Notch3 gene. In Drosophila melanogaster, Notch signaling has a pleiotropic effect, affecting most tissues of the organism during development. Objective: To characterize a potential mitochondrial dysfunction associated with mutations in the Notch3 gene. Methods: Biochemical, histochemical, molecular, and genetic analyses were performed on muscle biopsy specimens and fibroblasts obtained from patients of a Spanish family with CADASIL. Additional biochemical and molecular analyses of the N55e11 mutant of D. melanogaster were performed. Results: In muscle biopsy specimens, a significant decrease was found in the activity of complex I (NADH [reduced form of nicotinamide adenine dinucleotide] dehydrogenase), and in one patient, histochemical analysis showed the presence of ragged-red fibers with abnormal cytochrome c oxidase staining. Reduced fibroblast activity of complex V (ATP synthase) was found. Supporting data on patients with CADASIL, it was found that the mutation N55e11 in Drosophila decreases the activity of mitochondrial respiratory complexes I and V. Conclusions: Mitochondrial respiratory chain activity responds, directly or indirectly, to the Notch signaling pathway. Mitochondrial dysfunction in patients with CADASIL may be an epiphenomenon, but results of this study suggest that the pathophysiology of the disease could include a defect in oxidative phosphorylation.

Syndrome of encephalopathy, petechiae, and ethylmalonic aciduria

We report a boy 20 months of age with encephalopathy, petechiae, and ethylmalonic aciduria (EPEMA). Other clinical features were severe hypotonia, orthostatic acrocyanosis, and chronic diarrhea. Magnetic resonance imaging (MRI) of the brain demonstrated bilateral lesions in the lenticular and caudate nuclei, periaqueductal region, subcortical areas, white matter, and brainstem. Short and medium chain Acyl-CoA dehydrogenase and cytochrome c oxidase (COX) activities in fibroblasts were normal. Muscle histochemistry disclosed diffuse COX deficiency, and respiratory chain activities in muscle disclosed severe COX deficiency. Twelve other patients with similar clinical features have been reported. Muscle COX activity, studied only in four, demonstrated a clear-cut defect.