Loss-of-function mutations in the VLCFA transporter ABCD1 leads to X-linked adrenoleukodystrophy (ALD), one of the most frequently occurring peroxisomal disorders that involve progressive loss of myelin and early mortality; elevated VLCFA is detected in the blood of 99% of male patients, and is one of the diagnostic tools for ALD85. Here, ABCD1 is linked to X-linked adrenoleukodystrophy.