Urinary YKL-40 as a diagnostic biomarker for cystinosis.

Early diagnosis of cystinosis is critical to limit disease progression. YKL-40, a protein in the chitinase family, released by inflammatory cells, may be a useful biomarker for cystinosis. In a case-control study of 10 children with cystinosis and 20 without cystinosis, matched by age and baseline eGFR, we measured urine YKL-40, NGAL, and EGF. A lateral flow device (LFD) for YKL-40 was also developed and tested. Urine YKL-40 was over 200-fold higher in children with cystinosis (64.6 ng/mL [IQR: 23.4, 83.8]) compared with controls (0.3 [IQR: 0.3, 0.79]; P = 0.0001) with excellent diagnostic discrimination (AUC = 0.99) that was superior to other biomarkers. LFD measurements for YKL-40 showed similar results (AUC = 0.93). YKL-40 results were verified in 5 cystinosis patients, and YKL-40 staining was markedly higher in kidney biopsies from cystinosis patients than in healthy controls. Urine YKL-40 has excellent diagnostic potential for cystinosis, and point-of-care technologies may facilitate early screening and management of this disease.