Etiology and treatment of adrenoleukodystrophy: new insights from Drosophila

Abstract

Adrenoleukodystrophy (ALD) is a fatal progressive neurodegenerative disorder affecting brain white matter. The most common form of ALD is X-linked (X-ALD) and results from mutation of the ABCD1-encoded very long chain fatty acid (VLCFA) transporter. X-ALD is clinically heterogeneous, with the cerebral form being the most severe. Diagnosed in boys usually between the ages of 4 and 8, cerebral X-ALD symptoms progress rapidly (in as little as two years) through declines in cognition, learning, and behavior, to paralysis and ultimately to a vegetative state and death. Currently, there are no good treatments for X-ALD. Here we exploit the Drosophila bubblegum (bgm) double bubble (dbb) model of neurometabolic disease to expand diagnostic power and therapeutic potential for adrenoleukodystrophy. We show that loss of the Drosophila long/very long chain acyl-CoA synthetase genes bgm and/or dbb is indistinguishable from loss of the Drosophila ABC transporter gene dABCD1. Shared loss-of-function phenotypes for synthetase and transporter mutants point to a lipid metabolic pathway association with ALD-like neurodegenerative disease in Drosophila; a pathway association that has yet to be established in humans. We also show that manipulation of environment increases the severity of neurodegeneration in bgm and dbb flies, adding even further to a suite of new candidate ALD disease-causing genes and pathways in humans. Finally, we show that it is a lack of lipid metabolic pathway product and not (as commonly thought) an accumulation of pathway precursor that is causative of neurometabolic disease: addition of medium chain fatty acids to the diet of bgm or dbb flies prevents the onset of neurodegeneration. Taken together, our data provide new foundations both for diagnosing adrenoleukodystrophy and for designing effective, mechanism-based treatment protocols.