There is various answers and all depends on the healthy status of every patient. Patients with Sialidosis Type I might survive till 40 years old (usually known in population from Japan) and patients with Sialidosis Type II might survive till 10 years old (usually known in population from Italy).
Some relevant symptoms that can affect the daily life of every patient are: low vision, mioclonyas, seizures, ataxia, muscular disorders, among others.