When mutant huntingtin protein is expressed only in mouse cardiomyocytes (Pattison et al. 2008), the animals develop HF whereas knocking down huntingtin expression in mice (Zeitling et al. 1995) and in zebrafish (Lumsden et al. 2007) is embryonically lethal, resulting in defects in all three germ layers and in iron utilization, respectively. This evidence concerns the gene HTT and hydrops fetalis.