Sialidosis is a rare lysosomal storage disease with two distinct clinical phenotypes. Type I sialadosis is the milder form with onset of gait abnormalities, progressive vision loss, bilateral macular cherry-red spots, and myoclonus in the second or third decade. Ataxia and seizures have also been reported in type I patients. Type II has an earlier onset with coarse facial features, dysostosis multiplex, short stature, developmental delay, mental retardation and hepatosplenomegaly. Type II patients may also present with a congenital-onset form associated with ascites and hydrops fetalis prenatally, an infantile-onset form with the absence of symptoms at birth or a juvenile form that has onset in late childhood and a relatively milder phenotype. Seizures, myoclonus and renal involvement have also been documented in type II cases. The frequency of diagnosed sialidosis in the general population is estimated at approximately one in four million live births.