Dystrophin Hot-Spot Mutants Leading to Becker Muscular Dystrophy Insert More Deeply into Membrane Models than the Native Protein

Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity

Becker muscular dystrophy (BMD) is an X-linked neuromuscular disease attributable to mutations in DMD, leading to a deficient and less functional dystrophin, mainly in skeletal and cardiac muscle. Understanding the natural history of BMD is crucial for optimizing patient care and developing targeted treatments. Retrospective data were collected from 943 patients diagnosed with BMD based on a combination of clinical, biochemical and genetic criteria followed by 17 Italian neuromuscular centres. Patients' demographics, main signs and symptoms at BMD onset, neuropsychiatric comorbidities, age at loss of ambulation, cardiac left ventricular ejection fraction, pulmonary forced vital capacity and DMD mutations were collected. Disease milestones were analysed in specific DMD mutational groups. The median age at the last assessment was 26.0 (16.6-41.9) years, with a median age at diagnosis of 7.5 (4.0-14.0) years. In 55% of patients, the diagnosis was prompted by the incidental finding of hyperCKaemia. At the last assessment, 13.5% of patients had lost the ability to walk at a median age estimated by Kaplan-Meier analysis of 69 years. Thirty per cent of patients exhibited left ventricular impairment and 2.7% respiratory involvement. Ten per cent of patients carried out-of-frame mutations, 4% nonsense mutations and 86% in-frame deletions/duplications. The subset of in-frame deletions was classified further based on the specific mutations. Patients carrying del45-49 compared with del45-47 were associated with an earlier loss of ambulation (P = 1 × 10-4), whereas patients with del45-55 (P = 0.005), del48 (P = 0.02) and del48-49 (P = 0.02) were correlated with a later loss of ambulation compared with del45-47. Both del45-55 (P = 0.002) and del48 (P = 0.003) were significantly associated with decreased odds of developing a pathological left ventricular ejection fraction compared with del45-47. Our results contribute to a better understanding of the natural history of BMD and capture precious data in the era of emerging therapies. The knowledge of the specific DMD mutation might help to define a prognosis in a subset of BMD patients and will serve as a model for the design of future therapies.

A label-free approach for measuring interactions of proteins with lipid membranes

In this issue of Cell Reports Methods, Sadi et al. present a nuclear magnetic resonance approach for quantitative assessment of protein interactions with lipid membranes. It is sensitive, applicable to diverse membrane systems, covers a broad range of KDs, and does not require large amounts of material.

Genotype-phenotype correlation in Becker muscular dystrophy in Chinese patients

Large deletions and duplications are the most frequent causative mutations in Becker muscular dystrophy (BMD), but genetic profile varied greatly among reports. We performed a comprehensive molecular investigation in 95 Chinese BMD patients. All patients were divided into three subtypes: normal muscle strength (type 1) in 18 cases, quadriceps myopathy (type 2) in 20 cases, and limb-girdle weakness (type 3) in 57 cases. Nineteen cases (20.0%) had small mutations and 76 cases (80.0%) had major rearrangements, including 67 cases (70.5%) of exonic deletions and 9 cases (9.5%) of exonic duplications. We identified 50 cases (65.8%) of in-frame mutations, and 26 cases (34.2%) of frame-shift mutations. The frequency of deletion in exons 13-19 was 30.6% in type 1 patients, 9.7% in type 2 patients, and 10.4% in type 3 patients. The frequency of deletion in exons 45-55 was 28.6% in type 1 patients, 40.8% in type 2, and 50.0% in type 3 patients. All major rearrangements of DMD gene in type 1 patients were also observed in type 3 patients. Our study suggested that frame-shift mutation was not rare in Chinese BMD patients. Although no difference was observed on the forms of DMD gene mutations among the three types of patients, the mutation in proximal region of DMD gene has higher frequency for patients without weakness. Effect of exon skipping for DMD depends on the size and location of the mutation. Additional studies are required to determine whether exon-skipping strategies in proximal region of DMD gene could yield more functional dystrophin.