PSEN2 and hydrops fetalis: Moreover, genetic evidence also suggests that the Apo E4 (apolipoprotein E4) allele and variants in the presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes have close contact in the development of HF and AD (Pang and Baum, 2000; Van Uden et al., 2000; Li et al., 2006; Gianni et al., 2010; Iadecola, 2013).