The complex lipidome as a driver of tissue-specific pathology in adrenoleukodystrophy.

X-linked adrenoleukodystrophy (ALD) is an inherited peroxisomal disorder caused by pathogenic variants in the ABCD1 gene, encoding a peroxisomal membrane transporter required for the import of very-long-chain fatty acids (VLCFA) into peroxisomes for degradation. ABCD1 deficiency leads to VLCFA accumulation in plasma and tissues. The resulting disease has a highly variable clinical presentation. In males, this manifests as cerebral demyelination, progressive myelopathy, and adrenal insufficiency, alone or in combination. Women predominantly develop myelopathy, while cerebral disease and adrenal insufficiency are rare, occurring almost exclusively in cases of extreme X-inactivation skewing toward the mutant allele. The lipid-mediated mechanisms linking VLCFA accumulation to tissue-specific pathology remain incompletely understood. Here, we review evidence that VLCFA-containing complex lipids, rather than free VLCFAs alone, are central mediators of tissue-specific pathology in ALD and discuss the therapeutic implications of this lipid-centric perspective. VLCFAs are incorporated into a broad range of complex lipids, including phosphatidylcholines, lysophosphatidylcholines, cholesterol esters, triacylglycerols, sphingomyelins, ceramides, and plasmalogens. The degree of lipid dysregulation increases with acyl chain length and saturation. VLCFA-containing lipid species correlate with disease severity across all clinical phenotypes. In the brain, VLCFA-containing phosphatidylcholines accumulate before demyelination onset, cholesterol ester accumulation is associated with neuroinflammatory cascades, and plasmalogen depletion reflects early oxidative damage. In the spinal cord, VLCFA-containing myelin lipids are associated with non-inflammatory axonopathy, mitochondrial dysfunction, and microglial phagocytic activation. In the adrenal gland, VLCFA accumulation in cholesterol ester-rich lipid droplets impairs ACTH receptor signaling and sequesters cholesterol from steroidogenic pathways. Enzymatic regulators of VLCFA homeostasis, including ELOVL1, SCD1, and the omega-oxidation enzymes CYP4F2 and CYP4F3B, are potential therapeutic targets for substrate reduction. Plasma VLCFA-lipid profiles correlate with disease severity across all affected tissues, positioning lipidomic profiling as a potential clinical instrument for risk stratification and treatment monitoring. Secondary lipid mediators amplify primary VLCFA toxicity through distinct, cell-type-specific pathways. The near-exclusive occurrence of cerebral ALD and adrenal insufficiency in women with extreme X-inactivation skewing suggests that partial reduction of the VLCFA lipid burden, rather than complete normalization, may be sufficient to prevent severe disease manifestations. This has direct implications for substrate-reduction therapy development.