OPRM1 and hydrops fetalis: Among these we find genes such as DLL4, a Notch ligand implicated in arterial formation43; FGF14, which regulates the intrinsic excitability of cerebellar Purkinje neurons44; SLC6A15, a gene that modulates stress vulnerability through the glutamate system45; and OPRM1, a modulator of the dopamine system that harbors a HF derived loss of stop codon variant in the genetic pool of modern humans but not in that of extinct human species19.