Super test
The new DNA test will help to identify more than fifty genetic diseases in a short time
The new DNA test, developed by scientists from the Garvan Institute of Medical Research in Sydney together with colleagues from Australia, the UK and Israel, will allow faster and more accurate detection of a number of difficult-to-diagnose neurological and neuromuscular genetic diseases compared to existing analogues. With its help, the diagnosis of some genetic diseases, which sometimes took years, will be reduced to several days.
The diseases covered by the test belong to the group of diseases caused by exceeding the permissible number of short tandem repeats. There are many places in the human genome where identical sequences of "genetic letters" — nucleotides are located one after another (for example, ACTG—ACTG—ACTG—ACTG ...). Sometimes the number of such sequences in the chain can vary without dangerous consequences for the body, but if their number exceeds a certain limit, a dangerous disease occurs. For example, in the gene encoding the huntingtin protein, in the fourth chromosome of the human genome, there is a repeatedly repeated sequence "cytosine-adenine-guanine". If the number of its repetitions exceeds 36, a person suffers from Huntington's disease, and the more repetitions of the CAG group, the more severe the disease manifests itself. Fragile X chromosome syndrome, hereditary cerebellar ataxia, myotonic dystrophy, myoclonic epilepsy, amyotrophic lateral sclerosis and other diseases are associated with similar phenomena in other genes. "They are often difficult to diagnose because of the complex symptoms that patients face, the complex nature of these repetitive sequences and the limitations of existing genetic testing methods," says Ira Deveson, head of genomic research and senior author of the paper.
One of the patients who participated in the study first realized that something was wrong with him when he had unusual balance problems while learning to ski. It took a long time until doctors determined that the cause of this was a rare genetic disease known as CANVAS. "It was very disturbing to have symptoms that intensified over the years, up to the inability to walk without support. I've been taking test after test for over ten years and had absolutely no idea what was wrong. It was nice to finally confirm my diagnosis genetically, and it's nice to know that in the near future other people with such diseases will be diagnosed faster than me," he says.
The new test uses a highly sensitive method of nanopore DNA sequencing. The sequencing device targets about 40 genes that are known to be associated with similar diseases, it reads chains of repetitive DNA sequences and detects abnormally long ones among them. During the tests, the method successfully identified patients with a number of such diseases.
"The new test will revolutionize how we diagnose these diseases, because now we can test all disorders at once with a single DNA test and make a clear genetic diagnosis, helping patients avoid years of unnecessary muscle and nerve biopsies or risky treatments that suppress the immune system for diseases that actually have they don't exist," says one of the authors of the work, neurologist Kishore Kumar. The team expects that the new technology will be used in diagnostic practice over the next two to five years. One of the key steps towards this goal will be obtaining clinical accreditation of the method.
The study was published in the journal Science Advances (Stevanovski et al., Comprehensive genetic diagnosis of tandem repeat expansion disorders with programmable targeted nanopore sequencing).
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