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A very rare lysosomal storage disease which is the normosomatic form of sialidosis with characteristics of gait abnormalities, progressive visual loss, bilateral macular cherry red spots and myoclonic epilepsy and ataxia, that usually presents in the second to third decade of life. The prevalence is unknown but it is less frequent than sialidosis type 2. This disease is due to a mutation of the N-acetyl-alpha-neuraminidase-1 (NEU1) gene (6p21) encoding the lysosomal enzyme neuraminidase that initiates the degradation of sialoglycoconjugates in lysosomes. Mutations lead to a decrease in enzyme activity and consequently to an accumulation of sialyloligosaccharides in tissues. Disease severity is linked to level of residual neuraminidase activity in vivo and varies between patients. Inherited in an autosomal recessive manner.
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