The most common PED is called X-linked adrenoleukodystrophy (X-ALD [MIM: 300371]), which is caused by mutations in the ABCD1 gene, resulting in elevated levels of VLCFA, and most frequently presents with severe cerebral ALD or adrenomyeloneuropathy (AMN) [2]. The gene discussed is ABCD1; the disease is X-linked adrenoleukodystrophy.