Urinary Proteome Profiling by Several Methods Identifies Titin as the Most-Differentiating Noninvasive Urinary Biomarker of Disease Severity in Becker Muscular Dystrophy

Background: Beckers muscular dystrophy (BMD) is a clinically heterogeneous dystrophinopathy caused by in-frame mutations in the dystrophin gene, resulting in variable disease severity. This variability limits the effectiveness of standardized functional measures for tracking progression. Circulating biomarkers, including urinary titin fragments generated during muscle injury, offer a promising non-invasive approach for assessing disease status. Methods: Mass spectrometry-based urinary proteomic profiling identified titin fragments as candidate biomarkers of muscle injury in BMD. These titin fragments were validated by two independent methods, targeted mass spectrometry and ELISA, using subsets of ambulatory BMD, non-ambulatory BMD and age matched healthy volunteers. Results: Urinary titin levels were significantly elevated by 4.56-fold and 2.32-fold in ambulatory and non-ambulatory BMD patients, respectively, compared with healthy controls. Titin levels also distinguished ambulatory from non-ambulatory BMD patients, demonstrating potential utility for monitoring disease progression and therapeutic response. Conclusions: Urinary titin fragments represent a promising non-invasive biomarker for BMD, with potential applicability to related neuromuscular disorders and clinical trials evaluating disease progression and treatment efficacy.