What else is it called?
- GM2 Gangliosidosis Type 2
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What causes it?
Sandhoff Disease is an Inherited Metabolic Disorder which causes certain types of fats to build up in the brain and other organs. It is caused a problem in the HEXB gene. This gene is needed to ensure that two enzymes work properly. These enzymes are called Hex-A and Hex-B (their longer names are beta-hexosaminidase A and beta-hexosaminidase B) and they play an important role in your nervous system.
The enzymes are found in a part of your body’s cells which is known as the lysosome. This is the “recycling centre” of the cell. You may see in some information that Sandhoff Disease is called a Lysosomal Storage Disorder.
The enzymes break down fatty substances, sugars and some molecules which are linked to sugars. Hex-A helps to break down a fatty substance called GM2 ganglioside.
Because the enzymes do not work properly, different substances build up and become toxic. This mainly affects the nerve cells (neurons) in the brain and spinal cord. When GM2-Ganglioside builds-up it destroys the nerve cells, and this is what causes the signs and symptoms of Sandhoff Disease.
There are 3 types of Sandhoff Disease:
The infantile form is the most common and most severe form of Sandhoff Disease. Other forms have milder signs and are very rare.
How common is it?
Sandhoff Disease affects approximately 1 in every 300,000 people in Europe. It is more common in the Creole population of northern Argentina; the Metis Indians in Saskatchewan, Canada; and people with a Lebanese family history.
What are the signs and symptoms?
The signs and symptoms of the infantile form of Sandhoff Disease begin around the ages of 3 to 6 months. You are likely to see the infant’s development slowing down and notice a progressive weakness. Any motor skills such as sitting, crawling, and turning over will be lost, they may have feeding problems and develop an exaggerated startle response to loud noises.
This is a progressive disorder and mental and motor symptoms worsen with time. As the disorder progresses the infant may also experience:
- Vision loss
- Hearing loss, blindness
- Mental deterioration
- Heart murmur
- Permanent contraction of muscles
- Enlarged organs
- Bone problems
- Doll-like facial features
A special eye examination can reveal red spots in the eyes (cherry red spots).
The prognosis is poor and those with the infantile form of Sandhoff Disease usually live only into early childhood.
The other forms of Sandhoff Disease have varying ages of onset and usually have milder symptoms. These may include:
- Muscle weakness
- Loss of muscle coordination
- Movement problems
- Speech problems
- Mental illness
How is it diagnosed?
Sandhoff disease can be diagnosed by performing an enzyme assay to measure the levels of the Hex-A and Hex-B enzymes. Sandhoff Disease is very similar and has symptoms that are almost the same as another disorder called Tay-Sachs Disease. The test will be able to show the difference between the two. Further testing is available if required.
Can it be treated?
There is no specific treatment or cure for Sandhoff Disease. Any treatment given aims to provide relief for the symptoms that are present and to ensure the highest level of support and care for your child and for your family. There is ongoing research underway to try and find a treatment for this disorder.
Do my family need to be tested?
Sandhoff Disease can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.
If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.
If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.
Once you are diagnosed, you can speak to a genetic counsellor. They can explain how Sandhoff Disease is inherited. They can also tell you about genetic testing for the rest of your family.