PRG4 and arthritic joint disease: Quantification of jaw joint defects using an Osteoarthritis Research Society International (OARSI) scoring system (Pritzker et al., 2006) that we modified for zebrafish (Figure 4—figure supplement 2) confirmed that joint defects increased in severity during aging (Figure 4H), consistent with the progressive arthritis seen in Prg4-/- mice (Koyama et al., 2014; Rhee et al., 2005) and patients with CACP (Marcelino et al., 1999).