Urinary N-terminal fragment of titin is a marker to diagnose muscular dystrophy in patients with cardiomyopathy

The differential diagnosis of cardiomyopathy is important. It has been recently reported that urinary titin N (U-TN) is increased in patients with muscular dystrophy (MD), and is associated with muscular damage. We aimed to clarify whether U-TN is useful as a diagnostic tool for distinguishing MD from various cardiomyopathies [e.g. dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM)]. We measured and compared the U-TN/creatinine ratio (U-TN/Cr; pmol/mg/dl) in 278 control subjects and 331 patients with various cardiomyopathies (DCM, n = 199; sarcoidosis, n = 18; HCM, n = 86; amyloidosis, n = 15; Fabry disease, n = 6; MD, n = 7). The U-TN/Cr was significantly higher in MD patients than in patients with various cardiomyopathies and the control subjects (P < 0.001). From the ROC analysis, the U-TN/Cr (with a cut-off value of 8.7) identified MD with 100% sensitivity, 82% specificity, and an area under the curve (AUC) of 0.92 (95% CI 0.87-0.98, P < 0.001). The AUC of the U-TN/Cr that was able to predict MD was superior to those of U-TN, creatinine kinase, B-type natriuretic peptide, and troponin I. Urinary Titin-N is a novel marker to diagnose MD.