Background: ABCD1 is a peroxisomal ABC transporter whose dysfunction causes X-linked adrenoleukodystrophy (X-ALD). Results: β-Oxidation of C26:0 and C22:0 acyl-CoA esters is impaired in X-ALD. ABCD3 accounts for residual β-oxidation activity in X-ALD fibroblasts. Conclusion: ABCD1 mediates very l…