The 70-kDa peroxisomal membrane protein (PMP70) and the adrenoleukodystrophy protein (ALDP aka ABCD1) are half ATP binding cassette (ABC) transporters in the peroxisome membrane. They are involved in metabolic transport of long and very long chain fatty acids into peroxisomes. Mutations in the ALD gene result in the X-linked neurodegenerative disorder adrenoleukodystrophy (ALD; MIM:300100). ABCD1 deficiency impairs the peroxisomal beta-oxidation of very long-chain fatty acids (VLCFA) and facilitates their further chain elongation by ELOVL1 resulting in accumulation of VLCFA in plasma and tissues. While all patients with ALD have mutations in the ABCD1 gene, there is no general genotype-phenotype correlation. In addition to ABCD1, other genes and environmental factors determine clinical features of ALD (Kemp et al. 2012, Berger et al. 2014).