The lack of ABCD1 function impairs the transport of CoA-activated very long-chain fatty acids (VLCFAs, ≥ C22) into the peroxisomes for degradation via β-oxidation [4], resulting in the accumulation of VLCFAs in tissues and body fluids of X-ALD patients, most notably in severely affected tissues like the brain white matter and the adrenal cortex [5]. The gene discussed is ABCD1; the disease is X-linked adrenoleukodystrophy.