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Triplet Repeat Expansions

By Levi Clancy for Student Reader on

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There are numerous diseases which arise from expansions in (CAG)n repeats, which encode glutamine. In a coding region, a (CAG)n repeat expansion can either inactivate a protein or exhibit a dominant phenotype due to poly-glutamine's toxic effects; examples include Huntington Disease and Spinocerebellar Ataxia (SCA) type I. In a non-coding region, a (CAG)n repeat expansion can interfere with chromatin structure and disrupt transcriptional regulation, and/or exhibit a dominant phenotype by distracting splicing factors with the triplet repeat; examples include Myotonic Dystrophy, Fragile X Syndrome and other SCA forms.