Sphingolipidoses: expanding the spectrum of α-synucleinopathies

Although α-synuclein pathology is typically associated with Lewy body diseases and multiple systems atrophy, increasing evidence indicates that it also occurs in a group of lysosomal storage disorders termed sphingolipidoses caused by the incomplete degradation, and subsequent accumulation, of a class of lipids termed sphingolipids. Notably, a number of genes that cause sphingolipidoses are also risk genes for Lewy body diseases, suggesting aetiological links between these distinct disorders. In the present review, we discuss the sphingolipidoses in which α-synuclein pathology has been reported: Gaucher disease, Krabbe disease, metachromatic leukodystrophy, Tay-Sachs disease and Anderson-Fabry disease, and describe the characteristic clinical and pathological features of these disorders, in addition to the evidence suggesting α-synuclein pathology occurs in these disorders. Finally, we evaluate the pathological mechanisms that underlie these rare disorders, with particular attention to how the enzymatic deficiency, substrate accumulation, or both, could contribute to the genesis of α-synuclein pathology and the implications of this for Lewy body diseases.