It is unclear whether the divergent regulation of both RALDH1 and CYP26A1 reflects a genuine species difference in the transcriptional regulation of these enzymes or whether the etiology of HF may be a factor, since the guinea pig model of HF was elicited by pressure overload, whereas IDCM individuals had no overt hypertension. The gene discussed is ALDH1A1; the disease is hydrops fetalis.