Polyglutamine diseases are a family of inherited neurodegenerative conditions that each derive from a CAG triplet repeat expansion in a specific gene. A CAG segment is made up of a series of three DNA building blocks (cytosine, adenine, and guanine) that appear multiple times in a row. Polyglutamine diseases have an abnormal increase in the number of CAG repeats, which triggers a chain of events that will culminate with neuronal degeneration and cell death in specific brain areas. There are nine known polyglutamine diseases, including Huntington’s disease, spinocerebellar ataxia (SCA) types 1, 2, 3, 6, 7, 17; dentatorubral-pallidoluysian atrophy (DRPLA); and spinal and bulbar muscular atrophy.

Dr Marta Olejniczak and her colleagues in Poland have just published promising results using a genetic tool to silence the expression of mutated genes containing expanded CAG repeats. They demonstrated the efficacy of using a genetic tool called short hairpin ribonucleic acid (shRNA) to silence the expression expanded CAG repeats in different patient-derived cells used as models of different polyglutamine diseases. Using the same shRNA in four different cellular models they successfully silenced the expression of the mutant protein responsible for Huntington’s disease (huntingtin), DRPLA (atrophin-1), SCA3 (ataxin-3), and SCA7 (ataxin-7). This genetic tool proved to be specific and it did not induce undesired effects in other genes. These results are an important step toward the development of universal drugs for polyglutamine diseases with the use of shRNA as a tool to reduce CAG repeat expansions. However, further studies performed in more cells and animal models are necessary to get this strategy on road to the clinics.

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