The Diagnostic Potential of Urinary Titin Fragment in Neuromuscular Diseases.

Biomarkers are important for the diagnosis and follow-up of neuromuscular diseases. Creatine kinase (CK) is a widely used marker of active muscle damage; however, it is not suitable for assessing muscle mass loss. Therefore, additional biomarkers are required to monitor skeletal muscle damage and loss. Titin plays an essential role in the structure and function of muscle fibers. It provides stability and elasticity to the sarcomeres. During sarcomere damage, fragments of titin and other proteins are released from muscle fibers and can be detected in blood and urine. Urinary titin-N fragment (UTN) detection is a noninvasive method for assessing and monitoring the extent of muscle damage. In addition to muscular dystrophies, elevated UTN levels have been observed in patients with sarcopenia. The UTN level increased significantly during eccentric muscle strain, indicating muscle damage, whereas the concentric load was associated with only a minimal increase in UTN. As titin is also present in the heart muscle, UTN can help diagnose cardiomyopathies and predict disease prognosis. In summary, the detection of urinary titin fragments is a promising tool for diagnosing and monitoring neuromuscular and cardiac diseases. While both CK and UTN rise and are related in acute conditions, their relationship is less clear in chronic diseases where muscle tissue damage and muscle mass loss are combined.