ABCD1 and X-linked adrenoleukodystrophy: X-Adrenoleukodystrophy (X-ALD) and D-bifunctional protein (D-BF) deficiency (ORPHA300): X-ALD is a progressive peroxisomal disorder affecting adrenal glands, testes and myelin stability caused by mutations in the ABCD1 gene, which encodes for ALD protein.