HSD17B4 and histiocytoid cardiomyopathy: Under normal conditions, FGF21 loss had minimal effects on most cardiac FAO genes, except peroxisomal Ehhadh, Hsd17b4, and ER-residing Hacd1/2 (linked to congenital cardiomyopathy) (Fig. 5a, b, supplementary Fig. 18a–c).