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Lysosomal storage diseases are inherited multi-organ diseases caused by defects in enzymatic acid hydrolytic reactions in lysosomes resulting in accumulation of physiological substrates followed by cellular and organ damages. GM1 gangliosidosis, one of the lysosomal storage diseases, is a neurodegenerative disease caused by an autosomal reces-sively inherited disorder of catabolism by lysosomal acid β-galactosidase.25 The disease manifests progressive neuro-logical dysfunction, which results from the intralysosomal accumulation of the specific physiological substrate, GM1 (monosialotetrahexosyl ganglioside), and the subsequent destruction of neurons. The defect of β-galactosidase is caused by deleterious mutations of the GLB1 gene encoding this enzyme. At present, there is no effective treatment. In domestic animals, naturally occurring GM1 gangliosi-dosis or β-galactosidase deficiency has been reported in dogs,2,18,19,22,27,30 cats,3-5,7 calves,8 and sheep.1,20,23 In dogs, the disease has been reported in mixed Beagles,19 Englis