In trisomy 21 PAPP-A levels compared with the controls were significantly decreased at the end of the first trimester (median value: 2.7 mU/mL, p = 0.02 ) but not thereafter (45.8 mU/mL at the end of the second trimester and 120 mU/mL near the term). The gene discussed is PAPPA; the disease is trisomy 21.