Depending on the age and the diet of the patient, the branched-chain fatty acids are increased in Refsum disease (OMIM 266500), RCDP type 1 and 5, ZSDs, DBP, alpha-methylacyl-CoA racemase (AMACR, OMIM 614307), sterol carrier protein X (SCPx, OMIM 613724) and possibly ATP-binding cassette sub-family D member 3 (ABCD3) deficiency. This evidence concerns the gene SCP2 and Refsum disease.