What

The free sialic acid storage diseases are a spectrum of rare, inherited, neurodegenerative disorders that are a result of the abnormal accumulation of a compound known as sialic acid within the body. There are several forms of this disease ranging from the mildest type known as Salla disease to the most severe known as infantile sialic acid storage disease (ISSD).

Who

The sialic acid storage diseases are more common among people of Finnish and Swedish descent. Actual incidence numbers are not known. Males and females are equally affected.

Signs and Symptoms

The severity of symptoms depends upon the form of free sialic acid storage disorder. Children with free sialic acid storage diseases may present with any of the following:

• Unique coarse facial features with prominent forehead, flattened nasal bridge
  
• Progressive developmental delay
  
• Poor weight gain and growth (failure to thrive)
  
• Mental retardation with delayed speech
  
• Poor muscle tone and impaired walking ability
  
• Enlarged heart, liver, and spleen
  
• Seizures and abnormal limb movements

Possible Causes

The cause of free sialic acid storage diseases is a defect in a key protein that allows for transport of the sialic acid out of the body’s cells. Mutations on the DNA level result in impaired removal of cellular sialic acid with subsequent accumulation of sialic acid leading to disease. Sialic acid storage diseases are inherited in an autosomal recessive manner, meaning that an affected child must inherit two defective copies of this gene.

Diagnosis

Making the diagnosis of free sialic acid storage disease depends upon linking the characteristic facial features and developmental delays with specific blood tests. Your doctor can order a test that will measure the level of free sialic acid in the body. If these levels are high in the urine, the diagnosis is confirmed. Genetic analysis of blood screening for DNA mutations can also solidify the diagnosis. An imaging test such as a magnetic resonance image (MRI) of the head may be ordered to document changes in the white brain matter that can be seen early in the disease process.

Treatment

Unfortunately there is no known cure for the free sialic acid storage diseases. Providing good supportive care and involving the necessary developmental, language, and speech specialists for those with the mild forms is crucial.

Prognosis

Children with Salla disease progress to adulthood with mental retardation, difficulties walking, and many other neurological problems. Those who inherit the infantile form usually do not survive beyond early childhood as they most commonly succumb to respiratory infections.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Children Living with Inherited Metabolic Diseases (CLIMB)

http://www.climb.org.uk/

Good international support group for a broad category of diseases.

National Tay-Sachs And Allied Diseases

http://www.ntsad.org/

Learn more about lysosomal storage diseases.

gene Reviews

http://www.geneclinics.org/profiles/issd/

Nice, concise summary of relevant findings and genetic testing and counseling options.

The Lysosomal Storage Disease Network

http://www.lsdn.com/

Thorough website for a broad spectrum of related disorders.

Orphanet.com

http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=GB&Expert=834

International website geared to providing good general information.

About Lysosomal Storage Diseases

http://www.ldnz.org.nz/page2.html

New Zealand based website with good links to international support groups.

Google Search for Free Sialic Acid Storage Disease

References and Sources

Kleta, R. et al. (2003) Biochemical and molecular analyses of infantile free sialic acid storage disease in North American children. Am J Med Genet 120A:28-33.