Clinical consequences of defects in peroxisomal beta-oxidation

The disorders of peroxisomal beta-oxidation, which have been well characterised at the molecular level, include defects of acyl-CoA oxidase, defects of the D-bifunctional protein (D-BP) (including specific defects of its enoyl-CoA hydratase and D-3-hydroxyacyl-CoA dehydrogenase components), defects of the very-long-chain fatty acid (VLCFA)-CoA importer [X-linked adrenoleukodystrophy (ALD)] and alpha-methylacyl-CoA racemase deficiency. A survey of the clinical consequences of these defects indicates that defects in the acyl-CoA oxidase and D-BP can produce neonatal hypotonia, seizures in early infancy, retinopathy and progressive neurological dysfunction with leukodystrophy on imaging. Defects in the VLCFA-CoA importer and in the racemase do not produce disease until a long time after the neonatal period. However, again the clinical picture is dominated by neurological disease: impaired cognitive function with leukodystrophy in childhood X-linked ALD and retinopathy and neuropathy in racemase deficiency. It is difficult to escape the conclusion that defective peroxisomal beta-oxidation has effects (such as impaired neuronal migration in the developing brain), which are more serious than those produced by the accumulation of substrates (VLCFAs, pristanic acid) alone.