On balance, plasma apelin appears to increase in early-onset and severe pre-eclampsia, but whether this is the case in late-onset or mild disease is unclear.138,139,145 However, the placenta may not be the source of circulating apelin, so any rise in plasma concentrations may reflect a compensatory increase in production from other tissues due to hypertension. The gene discussed is APLN; the disease is Hypertension.