Nephrocystin and ciliary defects not only in the kidney?

Cystoproteins have been recognized to play a major role in the development of cystic kidney diseases (CKDs) via interaction with the cilia/centrosome complex. We highlight our present knowledge on nephrocystin as the defective protein in nephronophthisis type I. Nephrocystin has been localized to the ciliary transition zone not only of renal tubule cells but also of respiratory and retinal cilia. Thus, multi-system involvement as in Senior-Løken-syndrome (retinal degeneration plus nephronophthisis) can be explained by a functional ciliary defect in various tissues. In addition, we illustrate that ciliated respiratory cells have a high potential for diagnostics in CKDs and will further aid understanding of the underlying molecular mechanisms.