Intriguingly, the majority (14/20) of the identified key regulators belonged to cluster K1 (Fig. 3, K1, labeled in red), including HOXC13, MSX1, FOXN1, DLX1, ELF5, DLX4, DLX3, MSX2, ARID3A, MDFI, CUX2, CSDC2, BHLHE23, and VAX2. Many of these genes were previously identified as key regulators during HF cycling in humans and mice. This evidence concerns the gene MSX2 and hydrops fetalis.