ABCD1 and peroxisome biogenesis disorder: Song et al measured cholesterol concentrations in fibroblasts of Zellweger spectrum disorder (ZSD) and X‐linked adrenoleukodystrophy patients and found a remarkable accumulation of cholesterol in all cases.49 While this could be straight‐forwardly explained by a general malfunction of peroxisome metabolism in ZSD, the accumulation of cholesterol in ABCD1 deficiency remains unexplained.