X-linked adrenoleukodystrophy (X-ALD) is a neurometabolic disease caused by pathogenic variants in the ATP binding cassette (ABC) subfamily D member 1 (ABCD1) gene, which is located on the X chromosome (Xq28) and encodes the peroxisomal transporter of CoA-activated saturated very long–chain FAs (VLCFAs; ≥22 C atoms). The gene discussed is ABCD1; the disease is X-linked adrenoleukodystrophy.