(ORDO NEWS) — Scientists have developed a rapid genetic test that can diagnose a wide range of rare muscle and nerve disorders with near-perfect accuracy.
Tandem repeat diseases are a family of over 50 inherited diseases, including Huntington’s disease and amyotrophic lateral sclerosis (ALS), that occur when short DNA sequences are repeated too many times.
Tandem repeats can arise from errors in DNA replication, which are then passed on to subsequent generations. However, many of them are benign, and all living things have them in various forms and combinations, making them a useful tool for determining relationships between people, such as kinship or tracing the origin of infections.
But sometimes they occur in problem areas of our genomes.
Depending on where they appear, unusually long forms of these repetitive patterns can lead to neurological or neuromuscular degeneration. However, since 37 genes are known to be associated with short tandem repeat disorders, multiple tests may be required to determine which genes are responsible for a person’s symptoms.
For patients like John, one of the participants in the new study, it could take more than a decade to narrow down the options.
John was eventually diagnosed with Cerebellar Ataxia Neuropathy and Vestibular Areflexia Syndrome, or CANVAS for short. It is a neurodegenerative movement disorder that is associated with the expansion of repetitive DNA sequences in the RFC1 gene.
However, within this single gene alone, there are many ways of repeating short DNA sequences, making a complete diagnostic test difficult to perform.
I took test after test for over 10 years and got absolutely no answers to the question, what’s the matter,” says John.
Neurologist Kishore Kumar says he and his colleagues at the Garvan Institute for Medical Research in Australia call the stressful process a “diagnostic odyssey.” While patients like John wait years for an answer, their symptoms gradually worsen.
While there is currently no cure for tandem repeat disorders, early diagnosis can help patients manage symptoms and possibly halt disease progression, so a newly developed test should make a big difference for patients.
“This new test will completely change how we diagnose these diseases, as we can now check for all disorders at once with a single DNA test and make a clear genetic diagnosis,” says Kumar, “helping patients avoid years of unnecessary muscle or nerve biopsies for diseases that they don’t have, or risky, treatments that suppress their immune systems.”
The newly developed assessment is based on nanopore technology that can analyze long DNA or RNA fragments in known repetitive regions of the human genome.
Taking a single DNA sample from human blood, researchers can run nucleic acids through a protein nanopore, using changes in electrical current resulting from molecular interactions, to decipher in real time the sequences of 40 genes known to be associated with 25 tandem repeat diseases.
Among the 37 patients who were tested by this method, including John, all were correctly assigned to their neurogenetic disease.
“We correctly diagnosed all patients with known diseases, including Huntington’s disease, fragile X syndrome, hereditary cerebellar ataxia, myotonic dystrophy, myoclonic epilepsy, motor neuron disease, and others,” says genomist Ira Deveson, also of the Garvan Institute.
Modern gene sequencing tests require machines the size of refrigerators, while nanopore technology is no bigger than a stapler. In addition, it costs hundreds of thousands of dollars less, which means it can be easily scaled and distributed.
Now researchers are trying to get clinical approval of this method. They hope that in two to five years the diagnostic test will be used regularly.
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