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Rhabdoid Tumour Predisposition syndrome - what does it mean?
What is Rhabdoid Tumour Predisposition Syndrome?
Rhabdoid tumour predisposision syndrome (RTPS) is a condition which means that the child that has is is much more likely to develop rhabdoid tumours than other children of their age. Children with RTPS are likely to develop rhabdoid tumours.
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What does having RTPS mean?
The increased risk of developing rhabdoid tumours in children with RTPS is at its highest under the age of 5 years and then decreases. Some children can develop more than one rhabdoid tumour.
Not all children with RTPS will definitely develop a rhabdoid tumour, but they are at significantly higher risk of it.
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Older children and adults with RTPS are at increased risk of developing schwannomas (less aggressive tumours of nerves) as well.
It is not known why some individuals with RTPS develop rhabdoid tumours and others develop schwannomas but it is likely to be as a result of a combination of factors.
How common is it?
Rhabdoid Tumour Predisposition Syndrome is very rare in the general population. However, it affects around a third of children that have already been diagnosed with a rhabdoid tumour.
For every 3 children diagnosed with a rhabdoid tumours, on average, one will have RTPS.
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Typically, children with RTPS are more likely to be diagnosed at an earlier age than children with sporadic tumours.
In children with sporadic tumours, the mutation affects only the cells in the itself, but the mutation in the INI1 gene is not present in the rest of the cells in the body.
What causes Rhabdoid tumour presisposition Syndrome?
RTPS is caused by an alteration (or mutation) that has occurred within one just one gene. Specifically, the mutation affects a gene called the INI1 gene also known as SMARCB1, located on chromosome 22.
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The INI1 gene is acts to produce proteins that act as ‘tumour suppressors.’ This means healthy INI1 genes are there to help keep cells healthy and stop them from growing and dividing too quickly.
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In individuals with RTPS, one of their two copies of the INI1 gene is altered or damaged meaning they only have one healthy copy and one mutated copy (or very occasionally two damaged copies.)
The loss of one of the healthy INI1 genes in individuals with RTPS means that cells may be able to grow and divide without the regulation needed. This is how rhabdoid tumours then develop in individuals with RTPS.
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Very rarely, a mutation can occur on chromosome 19, known as a SMARCA4 mutation. This also leads to the development of a RTPS in a similar way.
Testing for Rhabdoid Tumour Predisposition Syndrome
The easiest way to test individuals for RTPS is from a sample of blood. Specific cells in the blood are then identified and used to remove genetic information from to analyse.
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The two copies of the INI1 gene are analysed to see if there is a mutation (alteration) of the gene genetically. If the mutation is present, then the individual has RTPS.
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This is especially effective if then compared with the mutation found in the tumour tissue of the affected child. Genetic material can be extracted from the tumour sample in a similar way to blood and then compared to the blood sample. If the blood sample does not contain the tumour causing mutation (that has been identified on the tumour), then clinicians confirm that the individual does not have RTPS.
Will my other children be affected?
It is unlikely that any siblings your child has will develop a rhabdoid tumour too.
However, in a small number of cases, they may be at increased risk. This would only be the case if your child with a rhabdoid tumour and RTPS had inherited it from either of you. If inherited, siblings would have a 1 in 2 chance of having RTPS too. It is very rare to have two members of the same family affected but not impossible.
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It is important to remember that the majority of children with rhabdoid tumours do not have RTPS and even those that do are unlikely to have inherited it from their parents.
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If an individual is found to have RTPS, family members can subsequently be tested via a blood sample to see if they have the mutation too or whether it was a new mutation which would mean no other family members would be affected.
As can be seen from the flow chart below, only about a quarter of cases of RTPS are thought to be inherited from the child's parents.
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Do Individuals with RTPS need monitoring if they are otherwise well?
Currently, there is no standard guidance for individuals with RTPs. However, it has been suggested that children should receive a baseline MRI and renal ultrasound at diagnosis and then a regular screening protocol set up with a the child’s doctor. Here, the risks, benefits and limitations to screening can be discussed.
Reproductive options
If an individual with RTPS is concerned about passing the disorder on to future children, there are a number of options that can be explored including prenatal diagnosis and even preimplantation genetic diagnosis (PGD) which is an IVF process that allows diagnosis before implantation.
My child has RTPS, has it been inherited or is it a new mutation?
Some children with RTPS have inherited an altered copy of the INI1 gene from a parent who carries the same genetic mutation.
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Usually however, the RTPS results from the development of a ‘new mutation’ in either the egg or sperm before a child has been conceived or in the cells of a developing fetus.
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If this is the case, your child would be the first child in their family to carry this genetic change, and family members should not be at increased risk of developing rhabdoid tumours themselves.
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All individuals with RTPS (carry the INI1 mutation in each cell in their body) however have a 50% chance of passing this on to their children (this is irrespective of whether they inherited it themselves or whether it was a new mutation).
The transmission of this condition is know as autosomal dominant – the child only needs one faulty copy of the gene to cause the problem.
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Children that inherit the altered copy of the gene will also have RTPS and be at increased risk of developing rhabdoid and other tumours. Children that do not inherit the altered gene will not be at increased risk.
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Investigations my child may need, explained.