The diagnosis can be established by measuring the above mentioned metabolites in plasma, demonstration of C27- bile acid intermediates in urine, enzyme activity analysis in skin fibroblasts and mutation analysis of the AMACR gene (for review on the diagnosis of peroxisomal disorders and distinction between AMACR deficiency and other peroxisomal disorders see Klouwer et al. [6]). The gene discussed is AMACR; the disease is alpha-methylacyl-CoA racemase deficiency.