COL4A2 and osteoarthritis: A recent study by Butterfield et al. identified 14 genes involved in osteoarthritis pathogenesis, including Pitx1, and functionally characterize 6 candidate human osteoarthritis genes (Unk, Josd1, Gsdme, Arhgap30, Ccdc6, and Col4a2) in mouse models (Butterfield et al., 2021), revealing the genetic basis for osteoarthritis.