With an incidence of approximately 1:4.000.000 life births in the Caucasian population, sialidosis is a very rare disease. The real prevalence of sialidosis is unclear. The approximate prevalence of 1/5,000,000-1/1,500,000 live births (types 1 and 2 combined) has been estimated.
It is a progressive, lysosomal storage disorder that is inherited in an autosomal recessive manner and is caused by mutations in neuraminidase 1 (NEU1) gene. Sialidosis can be categorised depending on the clinical presentation into type I (late onset, normosomatic type, residual NEU1-activity of approximately 1-5%) and type II (early onset, dysmorphic type, residual NEU1-activity of < 1%).
Type I-Sialidosis, as called Cherry-Red Spot Myoclonus Syndrome, is characterized by ataxia, myoclonus syndrome and bilateral tonic-clonic seizures (MS) and ophthalmological findings (macular cherry-red spots).
Type II-Sialidosis is divided into 3 subtypes: congenital/neontatal, infantile (onset 0-12 months and juvenile form (13 monts-20 years). The earlier it occurs the more fulminant it becomes and might be associated with hydrops faetalis, ascites and early death, or within the first year of life with symptoms such as coarsened facial features, enlargement of the spleen and liver, dysostosis multiplex, vertebral deformities and severe mental retardation.
NEU1