Impact of late-onset Pompe disease on participation in daily life activities: Evaluation of the Rotterdam Handicap Scale

With the recent approval of enzyme replacement therapy for Pompe disease, insight into the social consequences of this disorder becomes even more relevant. The aim of this study was to measure the impact of late-onset Pompe disease on participation in daily life activities and to evaluate the applicability of the Rotterdam Handicap Scale (RHS) for use in Pompe disease. Two hundred fifty-seven adult patients from different countries participated in the study. The mean RHS score was 25.9+/-6.5 on a scale of 9-36. Individual item scores were lowest for 'domestic tasks indoors', 'domestic tasks outdoors', and 'work/study'. The mean RHS score differed significantly between patients with and without respiratory support (22.9 vs. 28.5, p<0.001) and patients with and without a wheelchair (20.9 vs. 29.5, p<0.001). No differences in RHS score were found between countries. The RHS showed good internal consistency and excellent Test-retest reliability. A ceiling effect of 8% was present. We conclude that the RHS seems suitable for this patient population and that Pompe disease has a large impact on the participation in daily life activities, in particular on the ability of patients to fulfil their work or study.

[Misdiagnosis of mitochondrial myopathies: a study of 12 thymectomized patients]

INTRODUCTION

Myasthenia gravis and mitochondrial myopathies have common symptoms (fatigability, ophthalmoplegia) that could lead to diagnosis confusion.

METHODS

We systematically reviewed medical history and ancillary investigations regarding 12 patients (7F/5M, mean age 47+/-14 years) having a mitochondrial myopathy but who were previously misdiagnosed as autoimmune myasthenia gravis and in whom a thymectomy was performed.

RESULTS

Ocular palsy, ptosis and bulbar palsy were present in all patients. Limb fatigability was present in 9 cases. Symptoms were fluctuant but without remission. The misdiagnosis of myasthenia was based on the following arguments: 1) decremental EMG response (2 cases); 2) positive injectable anticholinesterase drugs test (3 cases); 3) partial response to oral anticholinesterase medications (2 cases); 4) AChR antibodies titer of 0.6 nM considered as positive (1 case). A multisystemic involvement was present in 5 patients: peripheral neuropathy (2 cases), deafness (2 cases), cardiopathy (3 cases), cerebellar involvement (2 cases) and myoclonia (1 case). The diagnosis of mitochondrial myopathy (at a mean age of 38+/-12 years) has been certified on the results of muscle biopsy showing mitochondrial proliferation (12 cases) and deleted mitochondrial DNA (8 cases).

CONCLUSIONS

In a patient presenting with oculomotor symptoms and muscle fatigability, progressive course and multisystemic involvement are major arguments for a mitochondrial myopathy. In the absence of relevant criteria arguing for Myasthenia Gravis (significant variability of muscle weakness, positive titer of anti-AChR or anti-MuSK antibodies, decremental EMG response), a muscle biopsy is required before indication of thymectomy to exclude a mitochondrial disease.

Essais thérapeutiques et maladies musculaires

Recent advances in knowledge of muscle diseases has opened new perspectives for clinical trials. Because of the small number of patients available for study and the requirement for homogeneous study groups, multicentric trials must be conducted on a national or international basis. Moreover, because of the variability of clinical course of muscle diseases therapeutic protocols must be preceded by an assessment of the natural history of the disease. Analytic methods available include manual testing, quantitative muscle testing (QMT), functional scales, and evaluation of cardiac and respiratory function. Based on experience acquired with earlier protocols, we present methodologies currently used and the difficulties encountered. We discuss the potential ways for improving therapeutic trials.

Clinical and histopathological aspects of central core disease associated and non-associated with RYR1 locus

We analysed the clinical, histochemical, ultrastructural and genetic data of patients affected by central core disease (CCD) studied during the last 20 years. From a total series of 86 CCD-families, we have identified 46 CCD families with RYR1 mutations (16 autosomal dominant, 8 autosomal recessive, 17 sporadic cases and 5 de novo mutations). Out of the other 40 CCD families, the RyR1 gene was entirely excluded in 7 families, by cDNA sequencing or linkage analysis, indicating a genetic heterogeneity of CCD.

Severe cardiac arrhythmias in young patients with myotonic dystrophy type 1

Cardiac tachyarrhythmias have rarely been studied in young patients with myotonic dystrophy type 1 (DM1). The authors observed major cardiac rhythm disturbances in 11 patients aged 10 to 18 years. Tachyarrhythmic events were more frequent than impulse conduction disorders. Wide variations in CTG expansion were observed among the population. Since physical exercise was a prominent arrhythmogenic factor, systematic exercise tests with EKG monitoring may be indicated in young patients with DM1.

Thymidine phosphorylase gene mutations in patients with mitochondrial neurogastrointestinal encephalomyopathy syndrome

The mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) syndrome is characterized by the association of gastrointestinal and neurological symptoms. It is a rare autosomal recessive mitochondrial disorder with multiple mitochondrial DNA deletions and/or depletion. It is caused by thymidine phosphorylase (TP) gene mutations resulting in a complete abolition of TP activity. We tested 31 unrelated patients presenting either with a complete MNGIE syndrome (8 patients), a severe intestinal pseudo-obstruction (10 patients), and multiple deletions and/or depletion of mitochondrial DNA (13 patients). All the tested patients presenting with a complete MNGIE had increased thymidine levels in plasma and urine, and no TP activity. The group with pseudo-obstruction syndrome had normal or partial reduction of TP activity. We found pathogenic mutations on TP gene only in the MNGIE syndrome group: all the MNGIE patients were compound heterozygous or homozygous for mutations in the TP gene. Eight of these mutations are yet unreported, confirming the lack of genotype/phenotype correlation in this syndrome. Enzymatic activity and thymidine level are thus rapid diagnosis tests to detect MNGIE affected patients prior to genetic testing for patients with gastrointestinal symptoms.

Danon's disease as a cause of hypertrophic cardiomyopathy: a systematic survey

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease caused by mutations in sarcomeric genes. However, extensive genetic screening failed to identify a mutation in about a third of cases. One possible explanation is that other diseases, caused by other genes, may mimic HCM.

OBJECTIVE

To investigate the possible involvement of Danon's disease, an X linked lysosomal disease, in a large population of patients with HCM.

METHODS

A population of 197 index cases was considered; 124 were subsequently excluded because of a mutation in sarcomeric genes and 23 because of autosomal dominant inheritance. Fifty index cases were therefore included in molecular analysis (direct sequencing) of the lysosome associated membrane protein 2 (LAMP2) gene responsible for Danon's disease.

RESULTS

Two new mutations leading to premature stop codons were identified in patients who evolved towards severe heart failure (< 25 years old): 657C>T and 173_179del. The prevalence was therefore 1% of the total population (two of 197) or 4% of enrolled index cases (two of 50). Interestingly, Danon's disease was responsible for half of the cases (two of four) with HCM and clinical skeletal myopathy but was not involved in isolated HCM (none of 41).

CONCLUSIONS

Danon's disease may be involved in patients with previously diagnosed as HCM. A diagnosis strategy is proposed. To distinguish HCM from Danon's disease is important because the clinical evolution, prognosis, mode of inheritance, and therefore genetic counselling are very different.

Clinical and histologic findings in autosomal centronuclear myopathy

Centronuclear myopathy (CNM) is a congenital myopathy characterized by chains of centrally located nuclei in a large number of muscle fibers. Clinically, an early-onset form was reported in several autosomal-recessive (AR) families and many sporadic patients, whereas a late-onset form was found in most autosomal-dominant (AD) families. The boundary between these two forms remains unclear, and the molecular basis of autosomal CNM is still unresolved. To better define the clinical and morphologic characteristics of autosomal CNM, the authors analyzed a series of 29 patients from 12 families. Two subgroups were identified in three AD families: two families had a relatively late onset of disease and a slow progression of diffuse weakness, whereas the third family, who had a similar clinical course, also presented a unique diffuse muscle hypertrophy. Two presumed AR families and seven sporadic patients were analyzed together, and three subgroups were identified: 1) an early-onset form with ophthalmoparesis; 2) an early-onset form without ophthalmoparesis; and 3) a late-onset form without ophthalmoparesis. Overall, 23 muscle biopsies were reviewed; a majority of patients had >20% central nuclei, fiber type 1 predominance, and a radial distribution of sarcoplasmic strands on oxidative stains. A marked endomysial fibrosis was observed in three sporadic patients with a relatively severe clinical course. The classification reported in this study will be useful for the diagnosis and the follow-up evaluation of patients with autosomal CNM and for the research into the molecular defects underlying the condition.

Intolérance à l’effort et rhabdomyolyses d’effort : étiologies et démarche diagnostique

Exercise intolerance, sometimes complicated by rhabdomyolysis is a frequent complaint of patients consulting in neuromuscular centers. It may be the main clinical manifestation of many metabolic myopathies and muscular dystrophies. The first step of diagnosis relies on the performance of in vivo metabolism investigations: forearm or bicycle ergometer exercise tests, phosphorus nuclear magnetic resonance spectroscopy. A few enzymatic defects may be directly assessed on blood samplings, in particular carnitine palmitoyltransferase deficiency; but muscle biopsy is necessary in most cases in order to precise the etiology. When CK levels are elevated at rest, a muscle CT scan should be performed in order to detect muscles fatty replacement suggestive of a muscular dystrophy; this diagnosis will be confirmed with immunohistochemical and western-blot analysis of muscle proteins. We present a description of the main metabolic myopathies manifesting by exercise intolerance with an overview of clinical and laboratory evaluation leading to diagnosis. Differential diagnosis are also discussed.

[Myopathy-lipomatosis associated with A8344G mitochondrial DNA mutation]

We report the clinical features of two unrelated patients, a 51-year-old woman and a 54-year-old man, presenting proximal myopathy with lipomatosis. In both patients, muscle biopsies showed numerous ragged-red fibers. Molecular analysis were performed with denaturating gradient gel electrophoresis (DGGE) on muscle, blood, hair, buccal and urinary cells. The A8344G mutation of the tRNA-lysine gene of the mitochondrial DNA was detected in all tissues at high levels (more than 80 p cent). None of the patients had a contributive family history, and signs of central nervous system involvement were absent. These observations confirm that lipomatosis may be encountered in mitochondrial disorders and is tightly associated with the A8344G mutation.

Histopathological differences of myotonic dystrophy type 1 (DM1) and PROMM/DM2

Muscle biopsy findings in DM2 have been reported to be similar to those in DM1. The authors used myosin heavy chain immunohistochemistry and enzyme histochemistry for fiber type differentiation on muscle biopsies. Their results show that DM2 patients display a subpopulation of type 2 nuclear clump and other very small fibers and, hence, preferential type 2 fiber atrophy in contrast to type 1 fiber atrophy in DM1 patients.

[Exploration of exercise intolerance by 31P NMR spectroscopy of calf muscles coupled with MRI and ergometry]

One hundred patients presenting with exercise intolerance or rhabdomyolysis episodes have been examined successively by 31P Nuclear Magnetic Resonance Spectroscopy (MRS) of leg plantar flexor muscles with exercise test. In all cases a muscle biopsy was performed. At the end of investigations, diagnosis of a metabolic myopathy was made in 33 patients: glycogenolysis or glycolysis deficiency in 8 cases, mitochondrial myopathy in 24 cases and CPT II deficiency in one case. Muscular dystrophy or congenital myopathy were diagnosed in 6 cases. No precise etiology could be found in 30 patients with either high CK levels or muscle biopsy abnormalities. Seven patients had rhabdomyolysis related to excessive physical activities. Twenty-four patients had functional symptoms. The principal MRS parameters used for diagnosis were the values of intracellular pH at the end of exercise and the time constant of phosphocreatine resynthesis during recovery. Lack of acidosis after exercise was observed in all patients with blockade of glycogenolysis or glycolysis. A slowing in phosphocreatine resynthesis was found in 66 p.cent of patients with definite mitochondrial myopathy. The specificity of these parameters were respectively 92.4 p.cent and 85.5 p.cent for the two groups. In conclusion (31)P MRS allows the detection of muscular glycogenoses with a sensitivity close to 100 p.cent. However, its sensitivity was lower for the detection of mitochondrial myopathies, as is also known for the other in vivo metabolic investigations, reflecting the heterogeneity of expression of mitochondrial abnormalities in a given muscle. The integration of imaging in the examination protocol may help to orientate towards the diagnostic of a dystrophy in some patients.

[Metabolic myopathies in adulthood. Features and clues for diagnosis]

Metabolic myopathies are due to deficiencies of energy production involving glycogen, lipid, or mitochondrial metabolism. Deficiency of sarcoplasmic calcium-ATPase is at the origin of Brody's syndrome. Patients may present with exercise intolerance, myoglobinuria or progressive muscle weakness. The first step of diagnosis relies on the performance of in vivo metabolism investigations: forearm or bicycle ergometer exercise tests, phosphorus nuclear magnetic resonance spectroscopy. A few enzymatic defects may be directly measured on blood sampling, but muscle biopsy is necessary in most cases in order to precise the etiology of the metabolic defect through enzymatic assays. We present a description of the main metabolic myopathies with an overview of clinical and laboratory evaluation leading to diagnosis.

Functional characterization of novel mutations in the human cytochrome b gene

The great variability of the human mitochondrial DNA (mtDNA) sequence induces many difficulties in the search for its deleterious mutations. We illustrate these pitfalls by the analysis of the cytochrome b gene of 21 patients affected with a mitochondrial disease. Eighteen different sequence variations were found, five of which were new mutations. Extensive analysis of the cytochrome b gene of 146 controls found 20 supplementary mutations, thus further demonstrating the high variability of the cytochrome b sequence. We fully evaluated the functional relevance of 36 of these 38 mutations using indirect criteria such as the nature of the mutation, its frequency in controls, or the phylogenetic conservation of the mutated amino acid. When appropriate, the mtDNA haplotype, the heteroplasmic state of the mutation, its tissue distribution or its familial transmission were also assessed. The molecular consequences of the mutations, which appeared possibly deleterious in that first step of evaluation, were evaluated on the complex III enzymological properties and protein composition using specific antibodies that we have generated against four of its subunits. Two original deleterious mutations were found in the group of seven patients with overt complex III defect. Both mutations (G15150A (W135X) and T15197C (S151P)) were heteroplasmic and restricted to muscle. They had significant consequences on the complex III structure. In contrast, only two homoplasmic missense mutations with dubious clinical relevance were found in the patients without overt complex III defect.

A non-ischemic forearm exercise test for the screening of patients with exercise intolerance

BACKGROUND

The forearm exercise test is a common investigation that allows detection of some metabolic myopathies. It is not completely standardized and, when performed in ischemic conditions, may induce rhabdomyolysis in patients with glycogenosis.

OBJECTIVE

To develop a standardized non-ischemic exercise test for a safe screening of patients with exercise intolerance.

METHODS

Twenty-six healthy subjects and 32 patients with exercise intolerance performed an isometric exercise at 70% of the maximal voluntary contraction during 30 seconds in non-ischemic conditions. Blood concentrations of creatine kinase, lactate, and ammonia were analyzed.

RESULTS

A nearly fourfold lactate rise was induced by exercise in healthy subjects. All patients with normal muscle biopsy showed values similar to those of healthy subjects. No significant lactate increase was observed in six patients with a myophosphorylase defect and one with a debrancher defect. Disparate lactate responses were observed in 14 patients with a mitochondrial myopathy. The blood lactate level at rest was abnormally high in four of these patients. The lactate surface normalized by the mechanical energy production was above the normal range in eight patients.

CONCLUSIONS

The authors propose a standardized non-ischemic grip test that overcomes the main drawbacks of the classic ischemic forearm exercise test. It provides a specific, efficient, and safe screening test for patients with exercise intolerance. Its sensitivity was very good for patients with a glycogenolysis defect but remains partial in patients with a mitochondrial disorder.