GPNMB and polycystic kidney disease: GPNMB is a type 1 transmembrane glycoprotein with several domains: the extracellular domain contains a N-terminal region (NTR) with a predicted core amyloid fragment (CAF)46, followed by a polycystic kidney disease (PKD) domain and a Kringle-like domain (KLD); the intracellular domain includes a lysosomal sorting motif (Fig. 6C, S5A).