A team of researchers have developed a new DNA test that can identify a range of neurological and neuromuscular genetic diseases quicker and accurately.
Researchers from Garvan Institute of Medical Research in Sydney and collaborators from Australia, UK and Israel have designed a DNA test that can diagnose over 50 genetic diseases caused by unusually-long repetitive DNA sequences in a person’s genes – known as ‘Short Tandem Repeat (STR) expansion disorders’.
This groundbreaking development has the potential to detect genetic diseases which otherwise would be difficult to diagnose due to complex symptoms, the challenging nature of these repetitive sequences and limitations of existing genetic testing methods.
“We correctly diagnosed all patients with conditions that were already known, including Huntington’s disease, fragile X syndrome, hereditary cerebellar ataxias, myotonic dystrophies, myoclonic epilepsies, motor neuron disease and more,” said Dr Ira Deveson, Head of Genomics Technologies at the Garvan Institute and senior author of the study.
The study was published in Science Advances.
Accurately diagnosing genetic diseases
“Current genetic testing for expansion disorders can be hit and miss. When patients present with symptoms, it can be difficult to tell which of these 50-plus genetic expansions they might have, so their doctor must decide which genes to test for based on the person’s symptoms and family history. If that test comes back negative, the patient is left without answers. This testing can go on for years without finding the genes implicated in their disease. We call this the ‘diagnostic odyssey’, and it can be quite stressful for patients and their families,” noted Dr Kishore Kumar, a co-author of the study and clinical neurologist at the Concord Hospital.
Dr Kumar further commented: “This new test will completely revolutionise how we diagnose these genetic diseases since we can now test for all the disorders at once with a single DNA test and give a clear genetic diagnosis, helping patients avoid years of unnecessary muscle or nerve biopsies for diseases they don’t have or risky treatments that suppress their immune system,”.
Repeat expansion disorders cannot be cured; however, a quicker diagnosis can help doctors identify and treat disease complications earlier, emphasising that a single test that can rapidly and accurately diagnose could be life-changing for patients with genetic diseases.
Scanning for known and novel diseases
By using a single DNA sample that is usually extracted from blood, the test works by scanning a patient’s genome using a technology called Nanopore sequencing.
Dr Deveson said: “We have programmed the Nanopore device to home in on the roughly 40 genes known to be involved in these disorders and to read through the long, repeated DNA sequences that cause disease. By unravelling the two strands of DNA and reading the repeated letter sequences (combinations of A, T, G or C), we can scan for abnormally long repeats within the patient’s genes, which are the hallmarks of the disease.
“In the one test, we can search for every known disease-causing repeat expansion sequence, and potentially discover novel sequences likely to be involved in diseases that have not yet been described.”
Furthermore, the Nanopore technology used in this test is also smaller and cheaper than standard testing, which the team of researchers hope will smooth its uptake into pathology labs.
“With Nanopore, the gene sequencing device has been reduced from the size of a fridge to the size of a stapler, and costs around $1000, compared with hundreds of thousands needed for mainstream DNA sequencing technologies,” noted Dr Deveson.
The team are aiming to see their new technology used in diagnostic practice within the next two to five years. One key step towards this achievement is to gain appropriate clinical accreditation for this method.
“Once accredited, the test will also transform research into genetic diseases,” said Dr Gina Ravenscroft, a co-author of the study and a researcher working on rare disease genetics at the Harry Perkins Institute of Medical Research.
“Adult-onset genetic disorders haven’t received as much research attention as those that appear in early life,” Dr Ravenscroft noted. “By finding more people with these rare adult-onset genetic diseases, and those who may be pre-symptomatic, we’ll be able to learn more about a whole range of rare genetic diseases through cohort studies, which would otherwise be hard to do.”
