Cystatin C in cerebrospinal fluid and multiple sclerosis

OBJECTIVE: A recent study using surface-enhanced laser desorption/ionization time-of-flight analysis of cerebrospinal fluid identified a 12.5 kDa truncated isoform of cystatin C (CysC) as a specific biomarker for multiple sclerosis (MS). METHODS: Surface-enhanced laser desorption/ionization time-of-flight analysis of cerebrospinal fluid samples from 43 MS patients and 46 healthy control subjects. RESULTS: Full-length CysC (13.4 kDa) concentration was similar in MS and control samples. The 12.5 kDa CysC protein was produced from full-length CysC by N-terminal cleavage during storage at -20 degrees C. INTERPRETATION: The 12.5 kDa CysC isoform is a storage-related artifact and is not useful as a diagnostic marker for MS.