A new era in genetic testing for HSP

What it means for HSPers

 

by Adrienne Sexton, Genetic Counsellor and A/Prof. Michael Fahey, Neurogeneticist (Neurogenetics clinic, Royal Melbourne Hospital)

 

What has changed in genetic testing for HSP?

HSP can be caused by a change in any of 50 or more genes. For many years, single gene testing for a few of the more common genes (spastin, REEP1 and atlastin) was available, and the test would look through the thousands of letters of DNA code in one of those genes, to identify a change. If a change is identified, sometimes it is clear that this will stop the gene from working and cause HSP, but sometimes the scientists and doctors cannot be sure whether it explains the HSP diagnosis.

This same principle of looking through the letters of the DNA code can now be applied to many genes at once, representing a huge increase in capability. This major leap forward in genetic technology is called Next Generation Sequencing (other names are panel testing, whole exome sequencing, and Massively Parallel Sequencing). Testing for most or all of the currently known HSP genes now costs about the same as the old tests for one gene at a time, and although testing still costs more than $1,000, is expected that costs will continue to decrease steadily over time. The testing can also be done more quickly. Some types of gene changes are not detected by this type of testing however, and it is very likely there are still undiscovered genes for HSP that may be able to be tested for eventually.

How do I access genetic testing?

Genetic testing can be arranged via a neurologist or Genetic service. You can find a Genetic service in your area by checking http://www.genetics.edu.au/Genetics-Services/genetic-counselling-services

Genetic testing may be free through a Genetic service, depending on many factors including your personal and family history of the condition. If a specific gene for HSP is already known in your family members, then a genetic test is often free of charge for relatives.

Several labs in Australia and overseas offer testing for many HSP genes at once at competitive prices. This can test many combinations of genes, but usually requires a Clinical Genetics specialist to specify a list of which genes should be analysed.

Why is it helpful to visit a Genetics/Neurogenetics service or Neurologist for advice?

At a genetics clinic, Clinical Geneticists, Neurologists, Neurogeneticists, and Genetic Counsellors work together to look at your particular symptoms and family history, and determine which genes might be most relevant for testing. This can be complex and it is important because HSP overlaps with some other conditions – a single gene problem can sometimes cause HSP or another condition, and it is commonly difficult to get a clear diagnosis from the clinical symptoms. A list of conditions sometimes overlapping with HSP includes:

• Ataxia (problems with balance and coordination)
• Mitochondrial conditions (affecting the ‘energy factories’ of the cells in our body)
• Cognitive decline (problems with memory, thinking and planning)
• peripheral neuropathy (problems with sensation in the hands and feet)
• Amyotrophic lateral sclerosis (motor neuron disease)
• Primary lateral sclerosis
• Charcot-Marie Tooth syndrome

Genetics services can also discuss with you the options for potentially having children who will not have HSP. This can be achieved through genetic testing during early pregnancy or via an IVF process, however these options rely on the exact HSP gene problem in the family to be identified first. Some people want to consider these options while other do not – it’s very personal.

Genetic testing has pros and cons, and a genetic counsellor can give you the right information to help you think about the issues and reach a decision that’s best for you. Different people in the family may feel differently about whether they want to know a genetic cause for HSP. It is important to think about whether now is the right timing for you, the possible implications for your family, and to have support in place as needed.

How can genetic testing for HSP help?

Genetic testing may or may not find a cause of HSP in you or your family. Genetic test results for HSP will not usually change your medical treatment or mean that a cure is available. However, it may be useful if it leads to a genetic cause being pinpointed because:

• It may well give you some peace of mind, especially if you have been misdiagnosed in the past or you have been told that you may have one of several conditions or possibly a complex of more than one condition
• The certainty that a positive genetic diagnosis provides helps your doctor, physio and other health professionals. While a genetic diagnosis helps doctors by categorically identifying whether or not someone has one or more of the particular gene changes being tested for, it needs to be remembered that there is no cure or treatment for HSP discovered as yet.
• It may increase the accuracy of information about symptoms and prognosis (although many types of HSP are quite variable even among members of the same family)
• It identifies the inheritance pattern and the chances of children or relatives inheriting or having HSP
• Relatives can fairly easily find out whether they have inherited HSP or not, as screening for a known family gene change is relatively quick and inexpensive
• If a genetic cause is known, then testing during pregnancy or before pregnancy via IVF becomes a real option.