During developmental and inflammatory processes, heavy chains (HCs) from the serum-derived proteoglycan inter-α-inhibitor (IαI) are covalently transferred to HA via the TSG-6 enzyme to form an HC-HA complex, which is similar to osteoarthritis and rheumatoid arthritis (Lauer et al., 2015; Torihashi et al., 2015). The gene discussed is TNFAIP6; the disease is rheumatoid arthritis.