Sialidosis: Main Page | Overview | Fact Sheet |

What is Sialidosis?

Sialidosis is one of seven identified Glycoprotein storage diseases. These inherited diseases are part of a larger group of disorders called Lysosomal storage diseases. Lysosomes are membrane-bound compartments found in the cells of the body. These compartments contain enzymes, which are responsible for the breakdown of many different oligosaccharides (long sugar chains.) These sugar chains are continuously made and broken down in our bodies, and this process is necessary for appropriate mental and physical development. Each enzyme in the lysosome is responsible for a certain step in the breakdown of the sugar chains.

When an enzyme is not working, it leads to the build up of the sugar chains in the lysosome. In Sialidosis, the specific enzyme that is absent is called alpha- neuraminidase. Theis build up of oligosaccharide sugars that is caused, is gradual and interferes with the correct function of the cell. It eventually leads to the clinical features of Sialidosis. Features tend to progress in severity over time.

In Sialidosis, the specific enzyme that is absent is called alpha-neuraminidase.

What are the clinical features of Sialidosis?

There are four different types of Sialidosis; type I, type II congenital, type II infantile, and type II juvenile. They are characterized by the age of onset and type of physical and mental manifestations.

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.)

How is Sialidosis inherited?

Sialidosis is not contagious and cannot be “caught.” It is a genetic condition, which means that it is caused by a change in the instructions that direct the way our bodies grow and develop. These instructions are called genes. People have two copies of all their genes, including the gene for Sialidosis (alpha- neuraminidase). One copy is inherited from the mother in the egg, and one from the father in the sperm.

Only when there is a change in the gene code is there a possibility that the disease will occur. For a person to have Sialidosis, they must inherit changes in both of their alpha-neuraminidase genes resulting in instructions that do not function properly. This is known as autosomal recessive inheritance.

For a couple to have a child with Sialidosis, both parents must have at least one changed copy of the alpha-neuraminidase gene which they both pass on to their child. Parents do not have control over which genes they pass on to their children.

If a person has one changed copy of the alpha-neuraminidase gene and one normal copy of the alpha-neuraminidase gene they are said to be a “carrier” of the condition and will not show any symptoms of Sialidosis. If two parents are both carriers, they have a 1 in 4 (25%) chance of having a child with Sialidosis in each pregnancy.

What testing is available to determine if my child or I have Sialidosis?

Testing for Glycoprotein storage diseases is typically performed in conjunction with a genetics evaluation. A genetics team takes into account the medical history and clinical features of a patient to determine what type of genetic testing is appropriate. For the diagnosis of an Glycoprotein storage disease, a urine test should show increased oligosaccharides. To determine if the patient has Sialidosis, the urine test should be followed by a blood test or skin biopsy. The blood or skin sample should show decreased amount of the enzymes alpha- neuraminidase.

For families who have had a child diagnosed with Sialidosis, prenatal diagnosis is available in future pregnancies by looking at alpha-neuraminidase activity through Chorionic Villus Sampling (CVS) or amniocentesis. Prenatal diagnosis by detection of alpha-neuraminidase gene changes is also available for families in which the responsible gene changes have been identified.

What type of treatment is available for Sialidosis?

Individuals with Sialidosis should have routine follow-up with Genetics, Neurology, Ophthalmology, and other specialists such as Nephrology as needed. Currently, there is no cure to stop the progression of symptoms of Sialidosis and treatment is aimed at addressing the individual problems as they arise.

For some Glycoprotein diseases, bone marrow transplant has been trialed as an experimental therapy but there are no conclusive results on the long term benefits. Ask your specialist for more information on this

Additional Resources

For a personal viewpoint of Sialidosis please visit Alexander’s Hope on ISMRD’s website.

Sialidosis: Main Page | Overview | Fact Sheet |