Natural history of brain lesions in X-linked adrenoleukodystrophy: On-again, off-again.

X-linked adrenoleukodystrophy (ALD) is the most common inherited leukodystrophy (1:15,000 birth incidence) and is caused by mutations in the ABCD1 gene leading to accumulation of very long chain fatty acids.1,2 The ALD genotype confers several independent but overlapping phenotypes: adrenal insufficiency, adrenomyeloneuropathy (an adult-onset spastic paraplegia and neuropathy syndrome), and cerebral ALD (cALD). The dreaded cALD phenotype is characterized by the appearance of inflammatory demyelinating brain lesions that manifest in only a subset of male patients (∼60% lifetime risk) with the majority of cases clustered in the first decade of life.1