Sialidosis, also known as mucolipidosis type I, is among the rarest Lysosomal Storage Disorder (LSD) classified as part of the glycoproteinoses. There are two clinically distinct sub-types of sialidosis, type I and type II.
The less severe form of the disorder, sialidosis type I, characterized by later onset, cherry red spots, progressive vision loss. These patients can also have other neurological symptoms such as ataxia and myoclonus, but typically have normal intelligence.
Type II is the more severe form of sialidosis. These patients usually have more physical findings than patients with type I, such as short stature, coarse features, thoracic kyphosis, and hepatosplenomegaly. Similar to the milder type I patients, individuals with type II may also have the cherry red spot, ataxia, and myoclonus. However, additional neurological symptoms are likely to be present in patients with type II.