SPP1 and cyst: The inflammatory mediator (Trostel et al., 2018) and renal disease biomarker (Khamissi et al., 2022; Kim et al., 2022; Steinbrenner et al., 2023) osteopontin (SPP1) was enriched in ECPKD (log2FC=1.22, adjusted P=6.26×10−63), as was Erb-B2 receptor tyrosine kinase 4 (ERBB4; log2FC=0.83, adjusted P=1.7×10−58), the expression of which modulates cyst growth in mice and human cyst epithelial cell lines (Streets et al., 2017; Zeng et al., 2014).