Sialidosis type 1 is an autosomal recessive disorder caused by bialleic NEU1 gene mutations. Patients with sialidosis type I present variable neurological and eye dysfunction and the progression rate is variable. The goal of this protocol is to assess the neurological and ophthalmological status of these patients and characterize the clinical and laboratory abnormalities in order to determine the natural history of the disease. Patients will be followed every 6 month with comprehensive clinical, neurological and ophthalmological examinations combined with neuropsychological, blood, radiological and electrophysiological tests.