Sialidosis is a very rare inherited metabolic disorder characterized by a deficiency of the enzyme alpha-neuraminidase. This disorder belongs to a group of disorders known as Lysosomal Storage Diseases. Alternately known as Mucolipidosis I, Sialidosis has long been characterized as being one of the Mucolipidoses. However, it is now believed to be more appropriately identified as an Oligosaccharide Storage Disease.

It depends on the type of Sialidosis as there are two types. Sialidosis I begins in adolescence and is a milder form of the disorder. Sialidosis II is the more severe form of the disorder and it can be present at birth or anytime during infancy.

Sialidosis I may include involuntary muscle contractions (myoclonus), red spots in the eyes (cherry-red macules), inability to coordinate voluntary movement (ataxia), tremors, impaired vision, night blindness, and seizures. Sialidosis II may be characterized by coarse facial features, bone malformations (dysostosis multiplex), abnormal enlargement of the liver and spleen (hepatosplenomegaly), mental retardation, profound abdominal swelling, lack of muscle tone (hypotonia), loss of muscle tissue (atrophy), and difficulty breathing (dyspnea).

Sialidosis is inherited as an autosomal recessive genetic trait. The absence of the enzyme caused by the gentic defect, results in the accumulation of certain complex carbohydrates (mucopolysaccharides) and fatty substances (mucolipids).

It is very rare and affects males and females in equal numbers. It is thought to occur in 1 in 250,000 live births in the United States. Sialidosis I seems more prevalent in Italian ancestry, while Type II may be more prevalent in people of Japanese descent.

Treatment generally consists of supportive medical treatment for symptoms. There are experimental therapies being developed such as bone marrow transplantation and gene therapy.