Sialidosis (Mucolipidosis I)

General Description

Sialidosis is characterized by a deficiency of the digestive enzyme, alpha-neuraminidase.

The lack of this enzyme results in an abnormal accumulation of complex carbohydrates known as mucopolysaccharides, and of fatty substances known as mucolipids. Both of these substances accumulate in bodily tissues.

There are four types of Sialidosis: Each type of Sialidosis is characterized by the age of onset and by the type of physical and mental manifestations of this disorder. Type I affects both sexes with equal frequency. For further details read the History and Overview.

  • Type I is the mildest form of Sialidosis, with a range of onset from anywhere between 8-25 years of age. Many of the characteristic features of lysosomal storage diseases including coarse facial features, hepatosplenomegaly (large liver and/or spleen), and dysostosis multiplex (abnormal bone formation that is found in multiple bones of the body) are absent. One presenting feature is cherry red spots on ophthalmology evaluation. Cherry red spots are spots on the retina that have storage of sugar chain, causing the remainder of the healthy retina to look brighter. Other presenting features include seizures, myoclonus (quick, non- rhythmic muscle contractions that can occur in any skeletal muscle) and other symptoms of nervous system dysfunction.
  • Type II Sialidosis has an earlier age of onset and more severe symptoms than type I. The congenital form of type II Sialidosis has an onset before birth and symptoms will be present in the newborn period. Often, these babies have hydrops (accumulation of fluid in the body) and do not survive the newborn period. Individuals that survive typically have mental retardation and severe hepatosplenomegaly. Facial features are coarse and dysostosis multiplex is present.

The infantile form of type II Sialidosis has an onset within the first year of life. These individuals have mental retardation, coarse facial features, dysostosis multiplex, and cherry red spots. Hepatosplenomegaly may be present. Unique to the infantile type is renal involvement that may range from structural to functional kidney problems.

The juvenile form of type II Sialidosis has an onset anywhere from 2–20 years. Facial features show a mild coarsening and there are less severe bone changes on x-ray. Mental retardation, myoclonus, and cherry red spots are present. Hepatosplenomegaly is typically absent. A distinguishing characteristic of the juvenile form is the presence of angiokeratomas (superficial blood vessel dilations over which wartlike growths occur).

Sialidosis is among the most rare Lysosomal Storage Diseases, affecting perhaps less than 1:4,000,000 worldwide and is thought to be more common in people with Italian ancestry.

  • • cherry red spot myoclonus syndrome
  • • mucolipidosis I
  • • mucolipidosis type I
  • • myoclonus cherry red spot syndrome

Medical and Research Information

  • Genetics Home Reference has good information on Sialidosis.
  • GeneTests: A list of labs who do testing for Salidosis.
  • Clinical Trials: A registry of federally and privately supported clinical trials conducted in the United States and around the world. This site gives information about each trial’s purpose, who may participate and the location.
  • PubMed: The most recent literature
  • OMIM: Technical information about the genetics of Sialidosis. OMIM is a site developed for scientists and medical specialists and contains both general and highly technical information. Access to this site is free.

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