An update on Becker muscular dystrophy

PURPOSE OF REVIEW

The purpose of this review is to summarise the recent developments in trial readiness, natural history studies, and interventional clinical trials for Becker muscular dystrophy (BMD).

RECENT FINDINGS

As several treatment concepts have claimed to convert patients with Duchenne muscular dystrophy (DMD) into a BMD phenotype, BMD itself has moved into the focus of clinical research. Natural history studies have helped to better characterize patients with BMD and the disease is now a target for interventional trials. In parallel, there have been advances in diagnostics and in the development of preclinical models.

SUMMARY

Despite increased collaborative efforts to improve trial readiness amongst patients with BMD, there is still a lack of long-term natural history data, and the broad spectrum of disease severity remains a challenge for well designed clinical trials.

Electrocardiographic Changes in Jordanian Patients With Becker Muscular Dystrophy

Background and aim Becker muscular dystrophy (BMD) is an X-linked disease caused by an in-frame mutation in the dystrophin gene, which is considered an allelic disorder to the most severe form of dystrophinopahies, Duchenne muscular dystrophy, which leads to skeletal and cardiac muscle involvement and results in dilated cardiomyopathy (DCM). The aim of this study is to present our ECG data and the significance of this data in the early detection of DCM in these patients. Methods This is a retrospective study. All patients known to the clinical Genetic Clinic and Queen Alia Heart Center in Jordan with a diagnosis of Becker muscular dystrophy from the year 2011-2022 are offered cardiac evaluation according to the guidelines, which included clinical assessment, electrocardiograph, and 2-D echocardiograph (echo) at the time of diagnosis and every five years thereafter once the initial assessment was normal. All the records were retrieved and analyzed. Results Fifty-three patients of all ages with genetically confirmed BMD were identified. Twelve had no record as they didn't attend any cardiac evaluation. Forty-one were under regular clinical follow-up. Two were excluded as they died, and another four had no recorded data in our center. Ultimately, 35 patients were included and studied. The mean age was 30.5 years ± 22.1, ranging from two to seventy-seven years of age. Twenty-seven (77%) had abnormal ECG. High voltage R wave in V2 and V1 was the most common finding, followed by repolarisation abnormalities and Q wave (43%, 17%, 13%, and 11% respectively). Incomplete right bundle branch block in 4% as well as R/S ratio >1.2. U wave abnormalities in 3% and sinus tachycardia were found in only one patient. Conclusion Cardiac surveillance for patients with Becker muscular dystrophy is mandatory after the age of 16. Q wave and repolarisation changes should be taken seriously as early signs of dilated cardiomyopathy, even if the echo is normal.

Case report: A rare case of left ventricular noncompaction in two Chinese siblings with becker muscular dystrophy caused by deletion of exons 10 to 12 in the DMD gene

Background

Becker muscular dystrophy (BMD) is an inherited X-linked recessive condition resulting from mutations of the DMD gene encoding dystrophin. Left ventricular noncompaction (LVNC) is a rare cardiomyopathy morphologically characterized by abnormal myocardial trabeculae and deep recesses in the left ventricle. LVNC in BMD patients has only rarely been reported.

Case report

In the present study, we identified a deletion mutation in exons 10 to 12 (EX10_12 del) of the DMD gene (reference sequence NM_004006.2) in two Chinese siblings with BMD and LVNC by high throughput targeted next-generation sequencing (NGS) and quantitative polymerase chain reaction (qPCR). The proband was a 22-year-old man admitted with dyspnea, abdominal distention, and polyserositis. It is noteworthy that both the proband and his younger brother manifested progressive muscular atrophy and creatine kinase (CK) elevation. Light and electron microscopy examination of muscle biopsies showed the typical features of dystrophinopathies. Cardiac magnetic resonance imaging and echocardiography demonstrated that both brothers had an enlarged left ventricle, LVNC, and reduced left ventricular ejection fraction. Finally, the proband underwent heart transplantation at age 26 with an event-free follow-up over 4 years post-transplantation.

Conclusion

This case further enriches our knowledge of the symptoms, genotype, cardiac performance, management, and prognosis of BMD patients complicated by LVNC. It is recommended that early comprehensive cardiac evaluation should be considered for patients with BMD to exclude LVNC, as this may have a significant impact on their prognosis.

Multidimensional Biomechanics-Based Score to Assess Disease Progression in Duchenne Muscular Dystrophy

(1) Background: Duchenne (DMD) is a rare neuromuscular disease that progressively weakens muscles, which severely impairs gait capacity. The Six Minute-Walk Test (6MWT), which is commonly used to evaluate and monitor the disease's evolution, presents significant variability due to extrinsic factors such as patient motivation, fatigue, and learning effects. Therefore, there is a clear need for the establishment of precise clinical endpoints to measure patient mobility. (2) Methods: A novel score (6M+ and 2M+) is proposed, which is derived from the use of a new portable monitoring system capable of carrying out a complete gait analysis. The system includes several biomechanical sensors: a heart rate band, inertial measurement units, electromyography shorts, and plantar pressure insoles. The scores were obtained by processing the sensor signals and via gaussian-mixture clustering. (3) Results: The 6M+ and 2M+ scores were evaluated against the North Star Ambulatory Assessment (NSAA), the gold-standard for measuring DMD, and six- and two-minute distances. The 6M+ and 2M+ tests led to superior distances when tested against the NSAA. The 6M+ test and the 2M+ test in particular were the most correlated with age, suggesting that these scores better characterize the gait regressions in DMD. Additionally, the 2M+ test demonstrated an accuracy and stability similar to the 6M+ test. (4) Conclusions: The novel monitoring system described herein exhibited good usability with respect to functional testing in a clinical environment and demonstrated an improvement in the objectivity and reliability of monitoring the evolution of neuromuscular diseases.

Decision-Making And Selection Bias in Four Observational Studies on Duchenne and Becker Muscular Dystrophy

BACKGROUND

Natural history data are essential for trial design in Duchenne (DMD) and Becker muscular dystrophy (BMD), but recruitment for observational studies can be challenging.

OBJECTIVE

We reviewed reasons why patients or caregivers declined participation, and compared characteristics of participants and non-participants to assess possible selection bias in four observational studies, three on DMD and one on BMD.

METHODS

Three pediatric DMD studies focused on cross-sectional cognitive function and brain MRI (DMDbrain, n = 35 and DMDperfusion, n = 12), and on longitudinal upper extremity function and muscle MRI (DMDarm, n = 22). One adult BMD study assessed longitudinal functioning (n = 36). Considerations for non-participation were retrospectively reviewed from screening logs. Age, travel-time, DMD gene mutations and age at loss of ambulation (DMDarm and BMD study only), of participants and non-participants were derived from the Dutch Dystrophinopathy Database and compared using nonparametric tests (p < 0.05).

RESULTS

The perceived burden of the protocol (38.2%), use of MRI (30.4%), and travel-time to the study site (19.1%) were the most frequently reported considerations for non-participation. Only few patients reported lack of personal gain (0.0- 5.9%). Overall, participating patients were representative for the studied sub-populations, except for a younger age of DMDarm study participants and a complete lack of participants with a mutation beyond exon 63.

CONCLUSION

Optimizing patient involvement in protocol design, improving MRI experiences, and integrating research into clinics are important factors to decrease burden and facilitate participation. Nationwide registries are essential to compare participants and non-participants and ensure representative observational research. Specific effort is needed to include patients with distal mutations in cognitive studies.

[A predictive analysis of the association between clinical phenotypes and genotypes in children with Becker muscular dystrophy/Duchenne muscular dystrophy]

OBJECTIVE

To study the association between clinical phenotypes and genotypes in children with Becker muscular dystrophy (BMD)/Duchenne muscular dystrophy (DMD) so as to provide a theoretical basis for disease management, gene therapy, and prenatal diagnosis.

METHODS

A retrospective analysis was performed for the clinical data and gene detection results of 52 children with BMD/DMD. Multiplex ligation-dependent probe amplification (MLPA) was used to detect the DMD gene. The children with negative results of MLPA were further screened by exon chip capture combined with next-generation sequencing (NGS). The mothers of 20 probands were validated by sequencing.

RESULTS

The pathogenic genes for BMD/DMD were detected in 50 children by MLPA and NGS, with a detection rate of 96%. Among the 52 children, 36 (69%) had gene deletion, 7 (13%) had duplication, and 7 (13%) had micromutation. Among the 43 children with deletion/duplication, 32 had DMD and 11 had BMD; 37 children (86%) met the reading frame rule, among whom 27 (96%) had DMD and 10 (67%) had BMD. All 7 children with micromutation had DMD.

CONCLUSIONS

The reading frame rule has an extremely high predictive value for DMD but a limited predictive value for BMD.

Laparoscopic gynecological surgery in an adult woman with Becker muscular dystrophy performed with sevoflurane with cisatracurium anesthesia: A case report

RATIONALE

Becker muscular dystrophy (BMD) and Duchenne muscular dystrophy (DMD) are progressive neuromuscular disorders caused by mutations in the dystrophin gene. The management of anesthesia in patients with BMD is complicated because they are highly sensitive to the conventional anesthetics such as volatile anesthetics and muscle relaxants. It is reported that anesthesia in patients with DMD is associated with several complications. However, a few case reports have been published on adult patients with BMD undergoing surgery with general anesthesia. Reports indicate that children with BMD may experience some serious complications with flurane-inhaled anesthesia. However, no study has yet shown that the use of flurane-induced anesthesia in adults with DMD carries high risks.

PATIENT CONCERNS

We describe a 56-year-old woman with BMD who was scheduled for laparoscopic hysterectomy and bilateral adnexectomy under general anesthesia due to a mass in the uterus. The patient was diagnosed with BMD 20 years back and reported that during this period, she was able to walk slowly with help during her daily life. Additionally, she also had a history of hypertension since 4 years and type 2 diabetes mellitus since 2 years.

DIAGNOSIS

The patient was postmenopausal and presented with abnormal uterine bleeding and elevated CA125. Abdominal ultrasonography revealed diffuse enlargement of the uterus and hypoechoic internal echoes. These findings were suggestive of diffuse adenomyosis with multiple uterine leiomyomas, which would have adverse effects later in her life. Therefore, the patient required surgery to address the symptoms and further confirm the diagnosis. The final diagnosis was confirmed by histopathological analysis.

INTERVENTIONS

The patient was scheduled for laparoscopic hysterectomy and bilateral adnexectomy. Anesthesia was induced and maintained by a combination of intravenous and inhalation anesthetic agents, particularly cisatracurium besilate and inhaled. sevoflurane.

OUTCOMES

The duration of anesthesia and postoperative period were uneventful. At the end of the operation, the patient had normal vital signs and was fully conscious. The patient was followed up for 8 months and no complications were noted during this period.

LESSONS

The combination of sevoflurane and cisatracurium besilate is a safe and effective method for the anesthetic management of adult patients with BMD scheduled for laparoscopic gynecological surgery. On the other hand, it is important to be aware of even rare complications of procedures, so that necessary precautions can be undertaken. Further investigations are necessary to determine the safe dosage of volatile anesthetics specifically for this clinical scenario so that anesthesiologists can use this combination method more accurately and precisely.

Natural history of cardiac function in Duchenne and Becker muscular dystrophies on home mechanical ventilation

Heart impairment is classical in dystrophinopathies and its management relies on medical drugs. Mechanical ventilation is used to treat respiratory failure, but can affect cardiac function. We aimed to investigate the natural history of cardiac function in patients with Duchenne (DMD) and Becker (BMD) muscular dystrophies on home mechanical ventilation (HMV).We reviewed the chart of DMD and BMD patients, followed in our institution, to obtain ventilation setting at HMV initiation and echocardiographic data at baseline and end follow up, as well as onset cardiac events and thoracic mechanical complication. We analyzed cumulative incidence of cardiac events as well as echocardiographic parameters evolution and its association with ventilation settings.We included 111 patients (101 DMD and 10 BMD). Median age was 21 years [18-26], median pulmonary vital capacity (VC) 15% of predicted [10-24]. All patients were on HMV and 46% ventilated using tracheostomy. After a median follow up of 6.3 years, we found a slight decrease of the left ventricular ejection fraction (LVEF) (45% at end follow up vs 50% at baseline P = .019) and a stabilization of the LV end diastolic diameter indexed (LVEDD indexed 29.4 mm/m vs 30.7 mm/m at end follow up, P = .17). Tidal volume (VT) level was inversely associated with the annual rate of the LVEF decline (r = -0.29, P = .025). Left atrium (LA) diameter decreased with mechanical ventilation (24 mm vs 20 mm, P = .039) and we found a reduction of systolic pulmonary pressure (35 mm Hg vs 25 mm Hg, P = .011). The cumulative incidence of cardiac events was 12.6%. Pneumothorax occurred in 4% of patients. Hypoxic arrest secondary to the presence of tracheal plugin occurred in 4% of patients with invasive ventilation.HMV is not harmful, decreases pulmonary pressure and may protect heart in dystrophinopathies, in addition with cardioprotective drugs. In patients with DMD and BMD on HMV, cumulative incidence of cardiac events remains moderate and incidence of pneumothorax is rare.

A case report with the peculiar concomitance of 2 different genetic syndromes

RATIONALE

Down syndrome (DS) is the most common chromosome disorder in live born infants, affecting several body systems, but usually sparing skeletal muscles. We present the case of a child with coexistence of DS and dystrophinopathy. Only 1 similar case has been reported so far.

PATIENT CONCERNS

An 8-year-old boy with DS had a history of incidental finding of increased serum creatine kinase levels up to 1775 U/L (normal values 38-174 U/L). He presented no delay in motor development; at the neurological examination, no muscle weakness or fatigability was detected in 2 different evaluations performed over a 6-month period.

DIAGNOSES

Skeletal muscle biopsy revealed marked dystrophic changes with patchy immunostaining for dystrophin. The Duchenne muscular dystrophy gene was screened for deletions by multiplex polymerase chain reaction, but no mutations were found. Sequence analysis of the Duchenne muscular dystrophy gene revealed a splice-site mutation c.1812+1G>A in intron 15 and confirmed a diagnosis of Becker muscular dystrophy.

INTERVENTIONS

The patient has started a specific physiotherapy that avoided any deterioration in motor development and muscular wasting.

OUTCOMES

A multidisciplinary follow-up was initiated. The genetician that followed the patient for DS was supported by the neurologist, the physiotherapist, the pulmonologist, and the cardiologist.

LESSONS

This peculiar "double trouble" case exemplifies the value of careful clinical evaluation and adequate clinical experience to identify the concomitance of 2 different genetic syndromes in the same patient, and it points out the significance of muscular strength assessment in DS patients to make the most correct prognosis, and, consequently, to organize the best long-term care.

Use of corticosteroids in a population-based cohort of boys with duchenne and becker muscular dystrophy

The use of corticosteroids for treatment of Duchenne and Becker muscular dystrophy in clinical practice from 1991 through 2005 was reviewed in a large population-based cohort (MD STARnet) of boys in 4 regional sites and 6 clinics of the United States. Corticosteroid use increased from 20% (11 of 56 individuals) in 1991 to 44% (93 of 218 individuals) in 2005. Average use varied by site and ranged from 15% to 49%. The median age of corticosteroid initiation was 6.9 years (range, 3.7-17.4 years). Dosage and growth information was available for 102 participants and showed a median dose as 0.729 mg/kg for prednisone and 0.831 mg/kg for deflazacort. T. The most common reasons that corticosteroids were discontinued included weight gain, behavioral side effects, and loss of ambulation, resulting in full-time wheelchair use. Substantial variations in clinical practice were identified among study sites.

The potential of exon skipping for treatment for Duchenne muscular dystrophy

Duchenne muscular dystrophy is mainly caused by mutations that disrupt the generation of a translatable mRNA transcript. Most such mutations occur in parts of the gene that are not essential for its function and thus might be eliminated from the transcript to permit translation of a partially functional protein that would convert the disease to a milder clinical form. Two such antisense oligonucleotides of different backbone chemistries have been successful when tested on the mdx mouse, targeting exon 23, containing the nonsense mutation. Subsequently, the morpholino, the more effective of these, has been tested on the dystrophic dog, where it is necessary to skip 2 exons, again with beneficial results. Currently, results of 2 human trials targeting exon 51 have also yielded promising preliminary results.

Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet): case definition in surveillance for childhood-onset Duchenne/Becker muscular dystrophy

The Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet) is a multisite collaboration to determine the prevalence of childhood-onset Duchenne/Becker muscular dystrophy and to characterize health care and health outcomes in this population. MD STARnet uses medical record abstraction to identify patients with Duchenne/Becker muscular dystrophy born January 1, 1982 or later who resided in 1 of the participating sites. Critical diagnostic elements of each abstracted record are reviewed independently by >4 clinicians and assigned to 1 of 6 case definition categories (definite, probable, possible, asymptomatic, female, not Duchenne/Becker muscular dystrophy) by consensus. As of November 2009, 815 potential cases were reviewed. Of the cases included in analysis, 674 (82%) were either ''definite'' or ''probable'' Duchenne/Becker muscular dystrophy. These data reflect a change in diagnostic testing, as case assignment based on genetic testing increased from 67% in the oldest cohort (born 1982-1987) to 94% in the cohort born 2004 to 2009.