What is Schindler Disease?
Schindler Disease 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 the 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 Schindler Disease, the specific enzyme that is absent is called alpha-N-acetylgalactosaminidase (previously known as alpha-galactosidase B.) The build up of oligosaccharide sugars that is caused, is gradual and interferes with the correct function of the cell. This build up is gradual and eventually leads to the clinical features of Schindler Disease. Features may progress in severity over time.
In Schindler Disease, the specific enzyme that is absent is called alpha-N- acetylgalactosaminidase (previously known as alpha-galactosidase B.)
What are the clinical features of Schindler Disease?
There are three different types of Schindler Disease. They are characterized by the age of onset and type of physical and mental manifestations.
Type I is called the infantile type of Schindler Disease. Typically, normal mental and physical development occurs during the first months of life. Between approximately 8-15 months, there is a rapid and severe regression in skills. Individuals with infantile Schindler disease usually have severe mental retardation, blindness, and/or seizures. Death typically occurs within the first 3-4 years of life.
Type II is the adult onset type of Schindler disease. This is characterized by angiokeratomas (superficial blood vessel dilation over which a wartlike growth occur), mild intellectual impairment, and peripheral nerve problems.
Type III is an intermediate and variable form of Schindler disease. It can range from a more severe presentation with seizures and mental retardation to a less severe form with speech/language delays, a mild autistic-like presentation, and/or behavioral problems.
How is Schindler Disease inherited?
Schindler Disease 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 Schindler Disease. 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 Schindler Disease, they must inherit changes in both of their alpha-N-Acetylgalactosaminidase genes resulting in instructions that do not function properly. This is known as autosomal recessive inheritance.
For a couple to have a child with Schindler Disease, both parents must have at least one changed copy of the alpha-N-acetylgalactosamindase 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-N-acetylgalactosaminidase gene and one normal copy of the gene, they are said to be a “carrier” of the condition and will not show any symptoms of Schindler Disease. If two parents are both carriers, they have a 1 in 4 (25%) chance of having a child with Schindler Disease in each pregnancy.
What testing is available to determine if my child or I have Schindler Disease?
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 Schindler Disease, the urine test should be followed by a blood test or skin biopsy. The blood or skin sample should show decreased activity of the enzyme alpha-N-acetylgalactosaminidase.
For families who have had a child diagnosed with Schindler Disease, prenatal diagnosis is available in future pregnancies by looking at alpha-N- acetylgalactosamindase activity through Chorionic Villus Sampling (CVS) or amniocentesis. Prenatal diagnosis by detection of alpha-N- acetylgalactosaminidase gene changes is also available for families in which the responsible gene changes have been identified.
What type of treatment is available for Schindler Disease?
Individuals with Schindler Disease should have routine follow-up with Genetics, Neurology, Ophthalmology and other specialists as needed. Currently there is no cure to stop the progression of symptoms of Schindler Disease, 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.