ABCD1 and X-linked adrenoleukodystrophy: Childhood cerebral X-linked adrenoleukodystrophy (X-ALD) is a rare, inherited neurodegenerative disorder caused by pathogenic mutations in the ATP-binding cassette sub-family D member 1 (ABCD1) gene, which encodes the peroxisomal membrane transporter adrenoleukodystrophy protein (ALDP).