Investigating myopathic causes of rhabdomyolysis

Rhabdomyolysis is an acute, and frequently severe, pathological event, characterized by rapid necrosis and destruction of striated muscle tissue. It is clinically characterized by muscle pain, weakness and emission of dark urine. The mechanisms that lead to rhabdomyolysis are various and different, and share common alterations such as dysfunction of the pumps Na + / K + and Ca2 + ATPase, and rupture of the sarcolemma, which in turn determine calcium homeostasis alterations, mitochondrial dysfunction, proteases activation, reduced availability of ATP and, overall, cell apoptosis and rhabdomyolysis. Several causes can initiate this vicious circle, both acquired and genetic. When facing an episode of rhabdomyolysis, the identification of the etiological cause can be extremely complex, long, and costly. Nevertheless, the correct identification of the underlying cause is of utmost importance for the correct information regarding prognosis (risk of recurrence) and for the family genetic counselling. Despite the application of extended diagnostic work up frequently it is not easy to distinguish if the rhabdomyolysis episode is due to a genetic disorder or whether it is the result of an abnormal effort, of an infectious episode or effect of a toxic. The main objective of this study is the evaluation of the diagnostic process of rhabdomyolysis, and to propose an updated, comprehensive, rational and cost effective protocol based on the latest information and techniques. We first studied the diagnostic process currently in use for rhabdomyolysis in a large retrospective study including 208 patients (aim 1). We characterized the clinical, molecular and radiological features of a new genetic cause of rhabdomyolysis, the CASQ1-related myopathy (aim 2). We determined the clinical spectrum of limb-girdle muscular dystrophy 2E (LGMD2E), investigating the risk of rhabdomyolysis of this disease (aim 3). We demostrated the role of EMG with provocative test (Long Exercise Test) as a sensitive and specific diagnostic test in the work up of rhabdomyolysis, especially in Glycogenosis type V (aim 4). We proposed a multi gene panel that should be studied by Next Generation Sequencing (NGS) in patients presenting rhabdomyolysis (aim 5) In conclusion, the results of this study suggest a new diagnostic algorithm for rhabdomyolysis. In this algorithm, the clinical features and few first-line tests (blood tests, EMG, acylcarnitines, grip test) exclude the most frequent causes or the treatable ones. The subsequent muscle biopsy will identify certain myopathies and guide toward the use of specific genetic panels for metabolic myopathies, muscular dystrophies or mitochondrial diseases that should be studied by NGS. The diagnostic algorithm that we propose will allow cost reduction and time optimization, and hopefully will increase the rate of etiological diagnosis of rhabdomyolysis, a serious event with major impact on patients' lives that, to date, remains poorly diagnosed

Genetic modifiers of Duchenne muscular dystrophy and dilated cardiomyopathy

OBJECTIVE: Dilated cardiomyopathy (DCM) is a major complication and leading cause of death in Duchenne muscular dystrophy (DMD). DCM onset is variable, suggesting modifier effects of genetic or environmental factors. We aimed to determine if polymorphisms previously associated with age at loss of independent ambulation (LoA) in DMD (rs28357094 in the SPP1 promoter, rs10880 and the VTTT/IAAM haplotype in LTBP4) also modify DCM onset. METHODS: A multicentric cohort of 178 DMD patients was genotyped by TaqMan assays. We performed a time-to-event analysis of DCM onset, with age as time variable, and finding of left ventricular ejection fraction 70 mL/m2 as event (confirmed by a previous normal exam < 12 months prior); DCM-free patients were censored at the age of last echocardiographic follow-up. RESULTS: Patients were followed up to an average age of 15.9 \ub1 6.7 years. Seventy-one/178 patients developed DCM, and median age at onset was 20.0 years. Glucocorticoid corticosteroid treatment (n = 88 untreated; n = 75 treated; n = 15 unknown) did not have a significant independent effect on DCM onset. Cardiological medications were not administered before DCM onset in this population. We observed trends towards a protective effect of the dominant G allele at SPP1 rs28357094 and recessive T allele at LTBP4 rs10880, which was statistically significant in steroid-treated patients for LTBP4 rs10880 (< 50% T/T patients developing DCM during follow-up [n = 13]; median DCM onset 17.6 years for C/C-C/T, log-rank p = 0.027). CONCLUSIONS: We report a putative protective effect of DMD genetic modifiers on the development of cardiac complications, that might aid in risk stratification if confirmed in independent cohorts

Non-neural phenotype of spinal and bulbar muscular atrophy: Results from a large cohort of Italian patients

Objective: To carry out a deep characterisation of the main androgen-responsive tissues involved in spinal and bulbar muscular atrophy (SBMA). Methods: 73 consecutive Italian patients underwent a full clinical protocol including biochemical and hormonal analyses, genitourinary examination, bone metabolism and densitometry, cardiological evaluation and muscle pathology. Results: Creatine kinase levels were slightly to markedly elevated in almost all cases (68 of the 73; 94%). 30 (41%) patients had fasting glucose above the reference limit, and many patients had total cholesterol (40; 54.7%), low-density lipoproteins cholesterol (29; 39.7%) and triglyceride (35; 48%) levels above the recommended values. Although testosterone, luteinising hormone and follicle-stimulating hormone values were generally normal, in one-third of cases we calculated an increased Androgen Sensitivity Index reflecting the presence of androgen resistance in these patients. According to the International Prostate Symptom Score (IPSS), 7/70 (10%) patients reported severe lower urinal tract symptoms (IPSS score >19), and 21/73 (30%) patients were moderately symptomatic (IPSS score from 8 to 19). In addition, 3 patients were carriers of an indwelling bladder catheter. Videourodynamic evaluation indicated that 4 of the 7 patients reporting severe urinary symptoms had an overt prostate-unrelated bladder outlet obstruction. Dual-energy X-ray absorptiometry scan data were consistent with low bone mass in 25/61 (41%) patients. Low bone mass was more frequent at the femoral than at the lumbar level. Skeletal muscle biopsy was carried out in 20 patients and myogenic changes in addition to the neurogenic atrophy were mostly observed. Conclusions: Our study provides evidence of a wide non-neural clinical phenotype in SBMA, suggesting the need for comprehensive multidisciplinary protocols for these patients. \ua9 2016 Published by the BMJ Publishing Group Limited

Targeted gene panel screening is an effective tool to identify undiagnosed late onset Pompe disease

Mutations in the GAA gene may cause a late onset Pompe disease presenting with proximal weakness without the characteristic muscle pathology, and therefore a test for GAA activity is the first tier analysis in all undiagnosed patients with hyperCKemia and/or limb-girdle muscular weakness. By using MotorPlex, a targeted gene panel for next generation sequencing, we analyzed GAA and other muscle diseasegenes in a large cohort of undiagnosed patients with suspected inherited skeletal muscle disorders (n = 504). In this cohort, 275 patients presented with limb-girdle phenotype and/or an isolated hyperCKemia. Mutational analysis identified GAA mutations in ten patients. Further seven affected relatives were identified by segregation studies. All the patients carried the common GAA mutation c.-32-13T > G and a second, previously reported mutation. In the subcohort of 275 patients with proximal muscle weakness and/or hyperCKemia, we identified late-onset Pompe disease in 10 patients. The clinical overlap between Pompe disease and LGMDs or other skeletal muscle disorders suggests that GAA and the genes causing a metabolic myopathy should be analyzed in all the gene panels used for testing neuromuscular patients. However, enzymatic tests are essential for the interpretation and validation of genetic results. (C) 2018 Elsevier B.V. All rights reserved.Peer reviewe

Quantitative value of aldosterone-renin ratio for detection of aldosterone-producing adenoma: The Aldosterone-Renin Ratio for Primary Aldosteronism (AQUARR) study

Background Current guidelines recommend use of the aldosterone\u2010renin ratio (ARR) for the case detection of primary aldosteronism followed by confirmatory tests to exclude false\u2010positive results from further diagnostic workup. We investigated the hypothesis that this could be unnecessary in patients with a high ARR value if the quantitative information carried by the ARR is taken into due consideration. Methods and Results We interrogated 2 large data sets of prospectively collected patients studied with the same predefined protocol, which included the captopril challenge test. We used an unambiguous diagnosis of aldosterone\u2010producing adenoma as reference index. We also assessed whether the post\u2010captopril ARR and plasma aldosterone concentration fall furnished a diagnostic gain over baseline ARR values. We found that the false\u2010positive rate fell exponentially, and, conversely, the specificity increased with rising ARR values. At receiver operating characteristics curves and diagnostic odds ratio analysis, the high baseline ARR values implied very high positive likelihood ratio and diagnostic odds ratio values. The baseline and post\u2010captopril ARR showed similar diagnostic accuracy (area under the receiver operating characteristics curve) in both the exploratory and validation cohorts, indicating lack of diagnostic gain with this confirmatory test (between\u2010area under the curve difference, 0.005; 95% CI, 120.031 to 0.040; P=0.7 for comparison, and 0.05; 95% CI, 120.061 to 0.064; P=0.051 for comparison, respectively). Conclusions These results indicate that the ARR conveys key quantitative information that, if properly used, can simplify the diagnostic workup, resulting in saving of money and resources. This can offer the chance of diagnosis and ensuing adrenalectomy to a larger number of hypertensive patients, ultimately resulting in better control of blood pressure

Distribution of Exonic Variants in Glycogen Synthesis and Catabolism Genes in Late Onset Pompe Disease (LOPD)

Pompe disease (PD) is a monogenic autosomal recessive disorder caused by biallelic pathogenic variants of the GAA gene encoding lysosomal alpha-glucosidase; its loss causes glycogen storage in lysosomes, mainly in the muscular tissue. The genotype-phenotype correlation has been extensively discussed, and caution is recommended when interpreting the clinical significance of any mutation in a single patient. As there is no evidence that environmental factors can modulate the phenotype, the observed clinical variability in PD suggests that genetic variants other than pathogenic GAA mutations influence the mechanisms of muscle damage/repair and the overall clinical picture. Genes encoding proteins involved in glycogen synthesis and catabolism may represent excellent candidates as phenotypic modifiers of PD. The genes analyzed for glycogen synthesis included UGP2, glycogenin (GYG1-muscle, GYG2, and other tissues), glycogen synthase (GYS1-muscle and GYS2-liver), GBE1, EPM2A, NHLRC1, GSK3A, and GSK3B. The only enzyme involved in glycogen catabolism in lysosomes is alpha-glucosidase, which is encoded by GAA, while two cytoplasmic enzymes, phosphorylase (PYGB-brain, PGL-liver, and PYGM-muscle) and glycogen debranching (AGL) are needed to obtain glucose 1-phosphate or free glucose. Here, we report the potentially relevant variants in genes related to glycogen synthesis and catabolism, identified by whole exome sequencing in a group of 30 patients with late-onset Pompe disease (LOPD). In our exploratory analysis, we observed a reduced number of variants in the genes expressed in muscles versus the genes expressed in other tissues, but we did not find a single variant that strongly affected the phenotype. From our work, it also appears that the current clinical scores used in LOPD do not describe muscle impairment with enough qualitative/quantitative details to correlate it with genes that, even with a slightly reduced function due to genetic variants, impact the phenotype

The Clinical Outcome Study for dysferlinopathy: An international multicenter study

Objective: To describe the baseline clinical and functional characteristics of an international cohort of 193 patients with dysferlinopathy. Methods: The Clinical Outcome Study for dysferlinopathy (COS) is an international multicenter study of this disease, evaluating patients with genetically confirmed dysferlinopathy over 3 years. We present a cross-sectional analysis of 193 patients derived from their baseline clinical and functional assessments. Results: There is a high degree of variability in disease onset, pattern of weakness, and rate of progression. No factor, such as mutation class, protein expression, or age at onset, accounted for this variability. Among patients with clinical diagnoses of Miyoshi myopathy or limb-girdle muscular dystrophy, clinical presentation and examination was not strikingly different. Respiratory impairment and cardiac dysfunction were observed in a minority of patients. A substantial delay in diagnosis was previously common but has been steadily reducing, suggesting increasing awareness of dysferlinopathies. Conclusions: These findings highlight crucial issues to be addressed for both optimizing clinical care and planning therapeutic trials in dysferlinopathy. This ongoing longitudinal study will provide an opportunity to further understand patterns and variability in disease progression and form the basis for trial design

Investigating myopathic causes of rhabdomyolysis

Rhabdomyolysis is an acute, and frequently severe, pathological event, characterized by rapid necrosis and destruction of striated muscle tissue. It is clinically characterized by muscle pain, weakness and emission of dark urine. The mechanisms that lead to rhabdomyolysis are various and different, and share common alterations such as dysfunction of the pumps Na + / K + and Ca2 + ATPase, and rupture of the sarcolemma, which in turn determine calcium homeostasis alterations, mitochondrial dysfunction, proteases activation, reduced availability of ATP and, overall, cell apoptosis and rhabdomyolysis. Several causes can initiate this vicious circle, both acquired and genetic. When facing an episode of rhabdomyolysis, the identification of the etiological cause can be extremely complex, long, and costly. Nevertheless, the correct identification of the underlying cause is of utmost importance for the correct information regarding prognosis (risk of recurrence) and for the family genetic counselling. Despite the application of extended diagnostic work up frequently it is not easy to distinguish if the rhabdomyolysis episode is due to a genetic disorder or whether it is the result of an abnormal effort, of an infectious episode or effect of a toxic. The main objective of this study is the evaluation of the diagnostic process of rhabdomyolysis, and to propose an updated, comprehensive, rational and cost effective protocol based on the latest information and techniques. We first studied the diagnostic process currently in use for rhabdomyolysis in a large retrospective study including 208 patients (aim 1). We characterized the clinical, molecular and radiological features of a new genetic cause of rhabdomyolysis, the CASQ1-related myopathy (aim 2). We determined the clinical spectrum of limb-girdle muscular dystrophy 2E (LGMD2E), investigating the risk of rhabdomyolysis of this disease (aim 3). We demostrated the role of EMG with provocative test (Long Exercise Test) as a sensitive and specific diagnostic test in the work up of rhabdomyolysis, especially in Glycogenosis type V (aim 4). We proposed a multi gene panel that should be studied by Next Generation Sequencing (NGS) in patients presenting rhabdomyolysis (aim 5) In conclusion, the results of this study suggest a new diagnostic algorithm for rhabdomyolysis. In this algorithm, the clinical features and few first-line tests (blood tests, EMG, acylcarnitines, grip test) exclude the most frequent causes or the treatable ones. The subsequent muscle biopsy will identify certain myopathies and guide toward the use of specific genetic panels for metabolic myopathies, muscular dystrophies or mitochondrial diseases that should be studied by NGS. The diagnostic algorithm that we propose will allow cost reduction and time optimization, and hopefully will increase the rate of etiological diagnosis of rhabdomyolysis, a serious event with major impact on patients' lives that, to date, remains poorly diagnosed.La rabdomiolisi è un evento patologico acuto e talvolta grave, caratterizzato da rapida necrosi e distruzione del tessuto muscolare striato alla quale corrisponde clinicamente dolore e debolezza muscolare ed emissione di urine scure. I meccanismi che portano alla rabdomiolisi sono vari e differenti ma condividono alterazioni comuni quali la disfunzione delle pompe Na+/K+ e Ca2+ ATPAsi, e la rottura del sarcolemma, che a loro volta determinano alterazioni dell’omeostasi del calcio, disfunzione mitocondriale, attivazione di proteasi, riduzione della disponibilità di ATP e, complessivamente, apoptosi cellulare e rabdomiolisi. La corretta identificazione della causa sottostante è di estrema importanza per una corretta informazione al paziente a fini prognostici (rischio di ricorrenza) e per il counseling genetico familiare. Nonostante l’applicazione di estesi work up diagnostici, non è sempre facile determinare se alla base di un episodio di rabdomiolisi vi sia una patologia genetica o se sia esclusivamente conseguenza di uno sforzo, di un episodio infettivo o dell’effetto di un tossico. L’obiettivo principale del presente studio è stato, pertanto, definire l’iter diagnostico ottimale in caso di rabdomiolisi, al fine di proporne uno aggiornato, completo, razionale ed economico che includa le più recenti nozioni e tecniche. Abbiamo inizialmente valutato l'iter diagnostico utilizzato ad oggi nei pazienti che presentano rabdomiolisi, in un ampio studio retrospettivo che ha incluso 208 pazienti (aim 1). Abbiamo quindi studiato le caratteristiche cliniche, radiologiche e molecolari di una causa genetica di rabdiomiolisi di recente identificazione, la miopatia da mutazoine nel gene CASQ1 (aim 2). Abbiamo in seguito valutato lo spettro clinico della distrofia dei cingoli tipo 2 E (LGMD2E), valutando il rischio di rabdomiolisi in tale patologia (aim 3). Abbiamo poi dimostrato il ruolo di EMG con test provocativi (Long Exercise Test) come test sensibile e specifico utilizzabile in pazienti affetti da rabdomiolisi, in particolare nella glicogenosi tipo 5 (aim 4). Abbiamo infine creato un pannello di geni che dovrebbe essere studiato mediante Next Generation Sequencin (NGS) in pazienti affetti da rabdomiolisi (aim 5). In conclusione, con le evidenze raccolte nel presente studio, proponiamo un nuovo algoritmo diagnostico per le rabdomiolisi. In tale algoritmo le caratteristiche cliniche e pochi test di primo livello (esami ematochimici, EMG, profilo delle acilcarnitine, “grip test”) permettono di escludere le cause più frequenti o trattabili. Tale algoritmo permetterà di contenere i costi ed ottimizzare i tempi della diagnosi, e auspicabilmente aumenterà il rate di diagnosi etiologiche della rabdomiolisi, un evento grave e con un notevole impatto sulla vita dei pazienti ma che ad oggi resta scarsamente diagnosticato