Genetic analysis of the X-linked adrenoleukodystrophy gene ABCD1 in Drosophila uncovers a conserved phenotype.

X-linked adrenoleukodystrophy (X-ALD) is a progressive neurodegenerative disorder caused by a loss-of-function (LOF) mutation in the ATP-binding cassette subfamily D member 1 (ABCD1) gene, leading to the accumulation of very long-chain fatty acids (VLCFAs). This disorder exhibits striking heterogeneity; some male patients develop an early childhood neuroinflammatory demyelination disorder, while other patients, including adult males and most affected female carriers, experience a chronic progressive myelopathy. Adrenocortical failure is observed in almost all male patients, with the age of onset varying, sometimes being the first diagnostic finding. The gene underlying this spectrum of disease encodes an ATP-binding cassette (ABC) transporter that localizes to peroxisomes and facilitates VLCFA transport. X-ALD is considered a single peroxisomal component defect and does not play a direct role in peroxisome assembly. Drosophila models of other peroxisomal genes have provided mechanistic insight into some of the neurodegenerative mechanisms with reduced lifespan, retinal degeneration, and VLCFA accumulation. Here, we perform a genetic analysis of the fly ortholog Abcd1 (CG2316). Knockdown or knockout of Abcd1 leads to salivary gland defects, reduced peroxisomal abundance, and VLCFA accumulation. Our null model further highlights locomotor impairment and lifespan abnormalities. Flies overexpressing the human cDNA for ABCD1, but not the fly Abcd1, display a wing crumpling phenotype characteristic of the Pex2 loss-of-function. Taken together, our data establishes the loss-of-function phenotypes for Abcd1 in Drosophila, which resemble X-ALD pathology, and suggests that overexpression of human ABCD1 may act as an inhibitor of peroxisomal biogenesis in flies. This fly model provides valuable insight into disease mechanisms and offers a versatile platform to model cerebral ALD, functionally resolve ABCD1 variants by their capacity to mitigate the biogenesis defect, assess the restorative potential of candidate small molecules, and enable discovery for this important disease.