Researchers from Australia’s Garvan Institute have joined with collaborators in Israel and the UK in identifying neuromuscular and neurological genetic diseases that have been difficult to diagnose due to the uniqueness of the repetitive sequences and the limitations of current methods of testing.
According to a recent article in Science Daily, the new test diagnosed patients with disorders that had already been established with accuracy. These conditions included Huntington’s disease, hereditary cerebella ataxias, motor neuron disease, and myotonic dystrophies.
The aforementioned disorders are among fifty diseases that result from DNA sequences called ‘Short Tandem Repeat expansion disorders.’ The tests will now be made available for pathology services worldwide.
After Ten Years of Being Tested
John, one of the study participants, had begun to notice symptoms ten years ago when he had difficulty keeping his balance during a skiing lesson.
His symptoms worsened until later in life, when he was unable to walk unsupported. After ten years of tests, he was diagnosed with cerebellar ataxia neuropathy and vestibular areflexia syndrome (CANVAS). It is a genetic disease that causes damage to the area of the brain that controls muscle coordination (cerebellum).
The genetic cause of the repeat expansion disorder was discovered in 2019. CANVAS was found to be the result of a repeat expansion in the protein-coding RFC1 gene. Repeat expansion disorders usually involve nerve and muscle damage.
There are over fifty genetic expansions. With current testing methods, doctors determine which genes they are going to test based on their patient’s symptoms. If the test result is negative then the patient does not have a diagnosis. This type of testing may continue indefinitely without discovering the causative genes.
The new test can now search for all disorders in one DNA test. The result is an accurate genetic diagnosis. The patients are saved from unnecessary biopsies and the risk of treatments that can accidentally suppress the immune system.
Doctors are still unable to cure repeat expansion disorders but accelerating the diagnosis will ensure treatment earlier.
About Nanopore Sequencing
A DNA sample, which is generally taken from a patient’s blood, is used to scan the patient’s genome through Nanopore sequencing technology.
The Nanopore technology has been developed to scan approximately forty genes believed to be associated with repeat expansion disorders.
The Nanopore system reads the long DNA sequences thought to be causing the disease. The scientists unravel the two DNA strands. By reading the letter sequences they can identify unusually long repeats in a person’s genes. The long repeats are the most typical features of the disorder.
In comparison, the new technology is much less expensive than mainstream DNA technologies. The difference in size would be a refrigerator versus a stapler.
The research teams plan to see their new technology accredited and in diagnostic practice within two to five years.
