Ana Cabello

CAPN3 mutations in patients with idiopathic eosinophilic myositis

Eosinophilic myositis (EM) constitutes a rare pathological entity characterized by eosinophilic infiltration of skeletal muscles, usually associated with parasite infections, systemic disorders, or the intake of drugs or L‐tryptophan. The exclusion of such causes defines the spectrum of idiopathic EM. Based on a protein analysis performed in one affected patient, we identified the gene encoding calpain‐3, CAPN3, as a candidate for a subset of idiopathic EM.

Genotypic and phenotypic features of McArdle disease: insights from the Spanish national registry

Background Published genotype/phenotype data on McArdle disease are limited in sample size. A single national (Spanish) registry of patients with McArdle disease was created with the purpose of analysing their genotypic and phenotypic characteristics. Methods A cross sectional study was conducted, collecting demographic, family history, clinical, genotype and functional capacity data from all patients diagnosed with McArdle disease in the Spanish National Health System up to December 2010. Results 239 cases were recorded (all of Caucasian descent, 102 women; mean±SD age 44±18 years (range 9, 93)); prevalence of ∼1/167 000 people. Two mutant PYGM alleles were identified in 99.6% of cases. Although there was heterogeneity in the severity of symptoms, there were four common diagnostic features: (1) 99.5% of patients reported a history of acute crises of exercise intolerance (accompanied by recurrent myoglobinuria in 50% of cases); (2) in 58% of patients, symptoms started in the first decade of life; (3) 86% of patients repeatedly experienced the ‘second wind’ phenomenon over life; and (4) 99% of patients had a high basal serum level of total creatine kinase (>200 U/l). Clinical presentation of the disease was similar in men and women and worsened with age. Patients who were physically active had higher levels of cardiorespiratory fitness (by 23%, p=0.003) and were more likely to improve their clinical course over a 4 year period compared with inactive patients (OR 225; 95% CI 20.3 to 2496.7). Conclusions The main clinical features of McArdle disease are generally homogeneous and frequently appear during childhood; clinical condition deteriorates with ageing. Active patients have a better clinical outcome and functional capacity.

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.

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.

Mitochondrial DNA deletion in a patient with mitochondrial myopathy, lactic acidosis, and stroke-like episodes (MELAS) and Fanconi's syndrome

Large-scale mitochondrial DNA deletion was found in a 5-year-old girl with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) and Fanconis syndrome. Muscle biopsy disclosed ragged-red fibers and cytochrome c oxidase negative fibers. Respiratory chain studies were normal. Southern blot analysis demonstrated a 10.5-Kb heteroplasmic deletion in both muscle and blood. Deleted genomes represented 40% of total mitochondrial DNA in muscle and 63% in blood. There was no evidence of point mutations characteristic of MELAS. We suggest that not only patients with progressive external ophthalmoplegia syndromes, but also those with defined syndromes [e.g., MELAS or myoclonic epilepsy and ragged-red fibers (MERRF)] without characteristic point mutations, be screened for mitochondrial DNA deletions.

Coenzyme Q 10 improves lactic acidosis, strokelike episodes, and epilepsy in a patient with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes)

Mitochondrial encephalomyopathies encompass a group of disorders that have impaired oxidative metabolism in skeletal muscles and central nervous system. Many compounds have been used in clinical trials on mitochondrial diseases, but the outcomes have been variable. It remains controversial whether treatment of mitochondrial diseases with coenzyme Q 10 is effective. This paper describes a case of mitochondrial myopathy, encephalopathy, lactic acidosis, strokelike episodes, and exercise intolerance successfully treated with coenzyme Q 10. Efficacy of this therapy in this patient is correlated to control of lactic acidosis and serum creatine kinase levels. Disappointingly, larger studies with coenzyme Q 10 failed to demonstrate a clear beneficial effect on the entire study population with regard to clinical improvement or several parameters of the oxidative metabolism. They suggest that the use of coenzyme Q in treatment of mitochondrial diseases should be confined to protocols. There is a confounding variation in phenotype and genotype, and the natural history of the disorders in individual patients is not accurately predictable. The unpredictable a priori efficacy of therapy suggests that a long-term trial of oral coenzyme Q may be warranted.

Severe infantile-onset cardiomyopathy associated with a homozygous deletion in desmin.

Desminopathy is a genetically heterogeneous disorder with autosomal dominant pattern of inheritance in most affected families; the age of disease onset is on average 30 years. We studied a patient with a history of recurrent episodes of syncope from infancy who later developed second-degree AV block and restrictive cardiomyopathy; she subsequently suffered several episodes of ventricular tachyarrhythmia requiring implantation of bicameral defibrillator. Neurological examination revealed rapidly progressive bilateral facial weakness, winging of the scapulae, symmetric weakness and atrophy of the trunk muscles, shoulder girdle and distal muscles of both upper and lower extremities. Muscle biopsy demonstrated signs of myofibrillar myopathy with prominent subsarcolemmal desmin-reactive aggregates. Molecular analysis identified a homozygous deletion in DES resulting in a predicted in-frame obliteration of seven amino acids (p.R173_E179del) in the 1B domain of desmin. We describe the youngest known desminopathy patient with severe cardiomyopathy and aggressive course leading to the devastation of cardiac, skeletal and smooth musculature at an early age.

Early-onset multisystem mitochondrial disorder caused by a nonsense mutation in the mitochondrial DNA cytochrome C oxidase II gene.

We report the first nonsense mutation (G7896A) in the mtDNA gene for subunit II of cytochrome c oxidase (COX) in a patient with early‐onset multisystem disease and COX deficiency in muscle. The mutation was heteroplasmic in muscle, blood, and fibroblasts from the patient and abundantly present in COX‐deficient fibers, but less abundant in COX‐positive fibers; it was not found in blood samples from the patients asymptomatic maternal relatives. Immunoblot analysis showed a reduced concentration of both COX II and COX I polypeptides, suggesting impaired assembly of COX holoenzyme.

Sporadic MERRF/MELAS overlap syndrome associated with the 3243 tRNALeu(UUR) mutation of mitochondrial DNA

We studied a patient with a mitochondrial encephalomyopathy characterized by the presence of all the cardinal features of both myoclonic epilepsy and ragged‐red fibers (MERRF) and mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) syndromes. Muscle biopsy showed ragged‐red fibers (RRF). Some RRF were cytochrome c oxidase (COX)‐negative, while some others stained positive for COX. Muscle biochemistry revealed defects of complexes I and IV of the respiratory chain. Both muscle and blood mitochondrial DNA from the patient showed the presence of the mutation at nucleotide position 3243 in the tRNALeu(UUR) gene and the absence of point mutations related to MERRF syndrome. The proportions of mutant mtDNA were 70% in muscle and 30% in blood. The mutation was absent in blood from all maternal relatives, in hair follicles from the mother, and in muscle from one sister of the proband. Therefore, there was no evidence of maternal inheritance.