Single test for over 50 genetic diseases to make diagnosis quicker

A team of international researchers have developed a new DNA test that can identify a range of hard-to-diagnose neurological and neuromuscular genetic diseases quicker and more-accurately than the existing tests.

"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 Ira Deveson, Head of Genomics Technologies at the Garvan Institute in Sydney.

The diseases covered by the test belong to a class of over 50 diseases caused by unusually-long repetitive DNA sequences in a person's genes, known as short tandem repeat (STR) expansion disorders. "They are often difficult to diagnose due to the complex symptoms that patients present with, the challenging nature of these repetitive sequences, and limitations of existing genetic testing methods," Deveson said.

The study, led by collaborators from Australia, the UK and Israel, and published in the journal 'Science Advances', shows that the test is accurate, and allows the team to begin validations to make the test available in pathology services around the world.

Further, the researchers noted that 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," said Kishore Kumar, clinical neurologist at Concord Hospital.

"This new test will completely revolutionise how we diagnose these 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," Kumar said.

Using a single DNA sample, usually extracted from blood, the test works by scanning a patient's genome using a technology called Nanopore sequencing. "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," Deveson said.

The team expects to see their new technology used in diagnostic practice within the next two to five years.