P.347Urinary titin fragment in Fukuyama congenital muscular dystrophy

Titin functions as a molecular spring during the relaxation-contraction cycle, connecting the Z and M lines in the sarcomere. Recently, ELISA systems were developed to quantify the N-terminal fragment of titin in urine. High excretion of titin into the urine of patients with Duchenne (DMD) and Becker (BMD) muscular dystrophies was revealed, suggesting urinary titin to be a potential diagnostic biomarker for DMD and BMD. In this study, we measured urinary titin concentrations in Fukuyama congenital muscular dystrophy (FCMD) patients and investigated its possible application as a biomarker. We measured urinary titin concentrations of 18 FCMD patients employing the Human Titin-N fragment Assay Kit-IBL (Immuno-Biological Laboratories Co. Ltd., Fujioka, Japan). Serum creatine kinase (CK) and motor function assessment by gross motor function measure (GMFM) were also determined during the period from shortly before to within 3 days after urine analysis. Correlations between those two clinical factors and urinary titin concentrations were assessed. Urinary titin concentrations of FCMD patients were significantly elevated as compared with those of normal controls. No data in this study were within normal range, whereas some DMD and BMD patients had parameters within normal ranges. The correlation between serum CK and urinary titin was significant, while that between GMFM and urinary titin was not. Urinary titin is a potential diagnostic biomarker for FCMD, though further accumulation of the data is still needed to decide whether or not this parameter actually reflects motor function.