In contrast, PDA cells subjected to low-oxygen conditions displayed reduced proliferation after just 24 h culture (Figure 1A), while substantially upregulating the characteristic hypoxia markers HIF-1α, hexokinase 2 (HK2) and N-Myc Downregulated protein 1 (NDRG1) (Figure 1B). The gene discussed is HIF1A; the disease is Patent ductus arteriosus.