The X-linked adrenoleukodystrophy (X-ALD) disorder is a peroxisomal disorder caused by a deficiency of adenosine triphosphate–binding cassette transporter protein (adrenoleukodystrophy protein) encoded by the adenosine triphosphate–binding cassette subfamily D member 1 (ABCD1) gene (OMIM 300371).1,2 The protein transports very long-chain acyl-CoA esters into peroxisomes, the site of very long-chain fatty acid (VLCFA) beta-oxidation.3 In patients with X-ALD, VLCFAs accumulate in all tissues, primarily affecting the central nervous system and adrenal cortex. The gene discussed is ABCD1; the disease is adrenoleukodystrophy.