Relative exchangeable copper: a new highly sensitive and highly specific biomarker for Wilson's disease diagnosis.

Wilson disease (WD) is an autosomal recessive inherited disorder of copper metabolism. Failure to diagnose WD can be dramatic leading to irreversible damages. The molecular genetic analysis of ATP7B gene is the reference test for diagnosis but the number of reported mutations of the ATP7B gene is on the rise. The analysis is cumbersome and requires tedious work. Other clinical and biological tests are proposed but it is often difficult to interpret some patients' results. A rapid and reliable biological test for WD diagnosis is still needed. Analytical reliability of Exchangeable copper (CuEXC) determination procedure is examined by studying the repeatability, the short term stability and stability in frozen serum. Relative exchangeable copper (REC=CuEXC/total copper%) is proposed and evaluated as a new diagnostic test and compared to classic tests used for WD diagnosis. Sixteen new Wilson disease patients were diagnosed in our institution between January 2009 and May 2011. The different biological tests used for WD diagnosis yielded lower sensitivity and specificity compared to our new biomarker, the REC. We show that REC is an excellent discriminatory tool for the diagnosis of WD offering 100% sensitivity and 100% specificity.