ABCD1 and X-linked adrenoleukodystrophy: X-linked adrenoleukodystrophy (X-ALD) is a complex disease where the same mutation in peroxisomal ATP binding cassette superfamily D gene (ABCD1) [1,2] can lead to clinically diverse phenotypes even in twin brothers, ranging from the fatal neuroinflammatory disorder of cerebral childhood ALD (cALD) to the adult disorder of adrenomyeloneuropathy (AMN) [3,4].