X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 (adenosine triphosphate (ATP)-binding-cassette transporter superfamily D member 1) gene encoding a peroxisomal ATP-binding cassette (ABC) transporter, ABCD1, which is responsible for entry of long chain fatty acids (VLCFAs; C26:0 and C24:0) into peroxisomes for degradation [144–147]. The gene discussed is ABCD1; the disease is X-linked adrenoleukodystrophy.