Parity ↑ risk of ACPA-negative RA in ages 18–44, OR 2.1 (1.4–3.2) but not in ages 45−70 years ↑ risk of ACPA-negative RA with young age (<23 years) at first birth, OR 2.5 (1.5–4.1) The gene discussed is PRTN3; the disease is rheumatoid arthritis.