Laurence Viollet

Gentamicin-induced readthrough of stop codons in duchenne muscular dystrophy

The objective of this study was to establish the feasibility of long‐term gentamicin dosing to achieve stop codon readthrough and produce full‐length dystrophin. Mutation suppression of stop codons, successfully achieved in the mdx mouse using gentamicin, represents an important evolving treatment strategy in Duchenne muscular dystrophy (DMD).

Effects of Angiotensin-Converting Enzyme Inhibitors and/or Beta Blockers on the Cardiomyopathy in Duchenne Muscular Dystrophy

Cardiomyopathy is a consequence of Duchenne muscular dystrophy (DMD). Suggested treatments include angiotensin-converting enzyme (ACE) inhibitors and/or β blockers (BBs), but few large series have been reported. We present 42 patients with DMD and cardiomyopathy treated with an ACE inhibitor or an ACE inhibitor plus a BB. Serial echocardiograms were recorded. Adequate ejection fractions (EFs) were obtained at initiation of therapy (EF <55%). ACE inhibitor dosage adjustments were made if a continued decrease in EF was noted. BB therapy was initiated when average heart rate on Holter monitoring exceeded 100 beats/min. Data were analyzed using paired t test and linear regression. Before ACE inhibition, patients (n = 22) demonstrated decreased EF over time (r(2) = 0.23). At ACE inhibitor therapy initiation, mean age was 14.1 ± 4.6 years and mean EF was 44.2 ± 6.8%. BB therapy was used in 24 of 42 patients. Mean age for the ACE inhibitor + BB group was 15.7 ± 3.9 years. The 2 groups showed significant improvement (p <0.0001 for ACE inhibitor and ACE inhibitor plus BB) compared to the pretherapy group. No significant differences were noted between treatment groups. Patients with DMD demonstrated a gradual decrease in myocardial function. Treatment with ACE inhibitor or ACE inhibitor plus BB resulted in significant improvement compared to pretherapy. No significant difference occurred in EF improvement between treatment groups. In conclusion, treatment with ACE inhibitor or ACE inhibitor plus BB can delay progression of cardiomyopathy.

Aminoglycoside-induced mutation suppression (stop codon readthrough) as a therapeutic strategy for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is the most common, lethal, X-linked genetic disease, affecting 1 in 3500 newborn males. It is caused by mutations in the DMD gene. Owing to the large size of the gene, the mutation rate in both germline and somatic cells is very high. Nearly 13-15% of DMD cases are caused by nonsense mutations leading to premature termination codons in the reading frame that results in truncated dystrophin protein. Currently there is no cure for DMD. The only available treatment is the use of glucocorticoids that have modest beneficial effects accompanied by significant side effects. Different therapeutic strategies have been developed ranging from gene therapy to exon skipping and nonsense mutation suppression to produce the full-length protein. These strategies have shown promise in the mdx mouse model of muscular dystrophy where they have been reported to ameliorate the dystrophic phenotype and correct the physiological defects in the membrane. Each of these molecular approaches are being investigated in clinical trials. Here we review nonsense mutation suppression by aminoglycosides as a therapeutic strategy to treat DMD with special emphasis on gentamicin-induced readthrough of disease-causing premature termination codons.

Re-examination of the Electrocardiogram in Boys With Duchenne Muscular Dystrophy and Correlation With Its Dilated Cardiomyopathy

Duchenne muscular dystrophy (DMD) results in dilated cardiomyopathy (DC). Characteristic electrocardiographic (ECG) changes include short PR interval, right ventricular hypertrophy (RVH), prolonged QTc interval, and prominent Q waves in leads I, aVL, V5, and V6 or in leads II, III, aVF, V5, and V6. We re-examined the prevalence and correlation of ECG changes with DC in DMD. Electrograms of 115 patients with DMD were evaluated. DC was defined as an echocardiographic ejection fraction<55%. PR interval and RVH were based on age-based normal values. Abnormal Q waves were >or=4 mm. Abnormal QTc interval was >or=450 ms. ST-segment depression was defined as >0.5 mm. Fishers exact test evaluated significant differences between groups and logistic regression determined whether number of ECG changes predicted DC. Forty had DC. No significant differences existed between the number of ECG changes in DC and non-DC groups (p=0.279). Distribution of findings included short PR interval (43%), RVH (37%), prominent Q waves in leads V5 (34%) and V6 (33%), prominent Q waves in leads I, aVL, V5, and V6 (3, 1 with DC), prominent Q waves in leads II, III, aVF, V5, and V6 (9, 4 with DC), long QTc interval (0), ST depression (2, 1 with DC), and flat/biphasic ST segments (38, 15 with DC). In conclusion, ECG changes are similar in patients with DMD regardless of presence of DC. Previously reported characteristic ECG changes are seen in a minority of DMD cases. The most common findings are short PR interval and RVH. Prominent Q waves in leads II, III, aVF, V5, and V6 are more likely.

Utility of cystatin C to monitor renal function in duchenne muscular dystrophy

Creatinine as a marker of renal function has limited value in Duchenne muscular dystrophy (DMD) because of reduced muscle mass. Alternative methods of assessing renal function are sorely needed. Cystatin C, a nonglycosylated protein unaffected by muscle mass, is potentially an ideal biomarker of nephrotoxicity for this population but requires validation. In all, 75 subjects were recruited: 35 DMD (mean age 10.8 ± 5.4 years, corticosteroids n = 19, ambulatory n = 26), 29 healthy controls, 10 with renal disease, and one DMD with renal failure. Cystatin C levels in DMD were normal irrespective of age, ambulation, or corticosteroid treatment. Serum cystatin C was 0.67 ± 0.11 mg/l compared to normal controls 0.69 ± 0.09. mg/l. In these same individuals serum creatinine was severely reduced (0.27 ± 0.12 mg/dl) versus normals (0.75 ± 0.15 mg/dl, P < 0.01). In one DMD subject in renal failure, cystatin C was elevated. This study demonstrates the potential value of cystatin C as a biomarker for monitoring renal function in DMD. Its applicability extends to other neuromuscular diseases. Muscle Nerve, 2009

KNEE EXTENSOR STRENGTH EXHIBITS POTENTIAL TO PREDICT FUNCTION IN SPORADIC INCLUSION-BODY MYOSITIS

Introduction: In this study we address the challenging issue of potential use of muscle strength to predict function in clinical trials. This has immediate relevance to translational studies that attempt to improve quadriceps strength in sporadic inclusion‐body myositis (sIBM). Methods: Maximum voluntary isometric contraction testing as a measure of muscle strength and a battery of functional outcomes were tested in 85 ambulatory subjects with sIBM. Results: Marked quadriceps weakness was noted in all patients. Strength was correlated with distance walked at 2 and 6 minutes. Additional correlations were found with time to get up from a chair, climb stairs, and step up on curbs. Conclusions: Quadriceps (knee extensor) strength correlated with performance in this large cohort of sIBM subjects, which demonstrated its potential to predict function in this disease. These data provide initial support for use of muscle strength as a surrogate for function, although validation in a clinical trial is required. Muscle Nerve, 2012

NATURAL HISTORY OF CARDIOMYOPATHY IN DUCHENNE MUSCULAR DYSTROPHY AND THE EFFECTS OF ANGIOTENSIN-CONVERTING ENZYME INHIBITOR WITH OR WITHOUT BETA-BLOCKER

Cardiomyopathy (CM) is an inevitable consequence of Duchenne muscular dystrophy (DMD). Suggested treatments include angiotensin-converting enzyme inhibitors (ACEI) and/or beta-blockers (BB), but few large series have been reported. We present 65 DMD patients with CM treated with ACEI or ACEIpBB