X-linked adrenoleukodystrophy: Clinical, metabolic, genetic and pathophysiological aspects

X-linked adrenoleukodystrophy (X-ALD) is the most frequent peroxisomal disease. The two main clinical phenotypes of X-ALD are adrenomyeloneuropathy (AMN) and inflammatory cerebral ALD that manifests either in children or more rarely in adults. About 65% of heterozygote females develop symptoms by the age of 60years. Mutations in the ABCD1 gene affect the function of the encoded protein ALDP, an ATP-binding-cassette (ABC) transporter located in the peroxisomal membrane protein. ALDP 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 have mutations in the ABCD1 gene, there is no general genotype-phenotype correlation. Environmental factors and a multitude of modifying genes appear to determine the clinical manifestation in this monogenetic but multifactorial disease. This review focuses on the clinical, biochemical, genetic and pathophysiological aspects of X-ALD. This article is part of a Special Issue entitled: Metabolic Functions and Biogenesis of Peroxisomes in Health and Disease.