Findings from the Longitudinal CINRG Becker Natural History Study

Multi-parameter quantitative magnetic resonance imaging for early detecting skeletal muscle involvement and predicting functional decline in children with Becker muscular dystrophy

BACKGROUND

The extreme clinical heterogeneity of children with Becker muscular dystrophy significantly poses a great challenge to accurately assess their disease status.

OBJECTIVE

To detect skeletal muscle involvement in children with Becker muscular dystrophy using multiple-parameter quantitative magnetic resonance imaging (qMRI), and to determine the preferred muscle site and qMRI biomarker.

MATERIALS AND METHODS

Fat fraction, T1, and T2 measurements were conducted in Becker muscular dystrophy (n=29) and healthy controls (n=23). North Star Ambulatory Assessment (NSAA) was performed in Becker muscular dystrophy. Group differences were compared by using the Mann-Whitney or Kruskal-Wallis test or a linear mixed-effect model. Receiver operating characteristic analysis with area under curve (AUC) was used to compare the diagnostic performance. Logistic regression was used to identify the predictor of functional decline.

RESULTS

Both fat fraction and T2 were effective in detecting muscle involvement across different functional stages that were categorized by NSAA, with fat fraction in gluteus maximus demonstrating the most superior diagnostic performance (AUC range, 0.85-0.98). The combination of T2 and T1 enables a good diagnosis of no abnormal fat-infiltrated muscles (AUC=0.82). Overall, fat fraction in gluteus maximus exhibited the strongest negative correlation with the NSAA score (r=-0.69, P<0.01) and emerged as an independent risk factor for functional decline (odds ratio=1.12, P=0.02).

CONCLUSION

Multi-parametric qMRI demonstrate effective capabilities for early detection of muscle involvement, with gluteus maximus being the preferred muscle site. Fat fraction in gluteus maximus may serve as a potential biomarker for predicting functional decline.

Increase in cathepsin K gene expression in Duchenne muscular dystrophy skeletal muscle

Dystrophinopathy is caused by alterations in the dystrophin gene. The severe phenotype, Duchenne muscular dystrophy (DMD), is caused by a lack of dystrophin in skeletal muscles, resulting in necrosis and regenerating fibers, inflammatory cells, and muscle fibrosis. Progressive muscle weakness is a characteristic finding of this condition. Here, we encountered a rare case of a 10-year-old patient with asymptomatic dystrophinopathy with no dystrophin expression and investigated the reason for the absence of muscle weakness to obtain therapeutic insights for DMD. Using RNA-seq analysis, gene expression in skeletal muscles was compared among patients with asymptomatic dystrophinopathy, three patients with typical DMD, and two patients without dystrophinopathy who were leading normal daily lives. Cathepsin K (CTSK), myosin heavy chain 3 (MYH3), and nodal modulator 3-like genes exhibited a >8-fold change, whereas crystallin mu gene (CRYM) showed a <1/8-fold change in patients with typical DMD compared with their expression in the patient with asymptomatic dystrophinopathy. Additionally, CTSK and MYH3 expression exhibited a >16-fold change (P < 0.01), whereas CRYM expression showed a <1/16-fold change (P < 0.01) in patients with typical DMD compared with their expression in those without dystrophinopathy. CTSK plays an essential role in skeletal muscle loss, fibrosis, and inflammation in response to muscles injected with cardiotoxin, one of the most common reagents that induce muscle injury. Increased CTSK expression is associated with muscle injury or necrosis in patients with DMD. The lack of muscle weakness in the patient with asymptomatic dystrophinopathy might be attributed to the low CTSK expression in the muscles. To the best of our knowledge, this is the first report to demonstrate that CTSK expression was significantly higher in the skeletal muscles of patients with DMD with a typical phenotype than in those without dystrophinopathy.