several ways (2). First, repeat units may serve as binding sites for transcription factors. The number of binding sites determines the rate of transcription. Second, the expansion and shrinkage of TRs can change the distance between two functional elements. Third, TRs can affect chromatin structure and consequently mediate transcription (2). A correlation between TR enrichment and nucleosome-depleted regions suggests that TRs mediate transcription by inhibiting nucleosome formation (7). Finally, frequent deletions of mononucleotide repeats in 30 or 50 untranslated regions (UTRs) were observed in tumors with microsatellite instability. This observation also suggested that mononucleotide repeats in 30 or 50 UTRs may perform specific functions (8). Currently, it is accepted that the number of units in trinucleotide repeats in both coding and non-coding regions is a crucial factor in the development of neurodegenerative diseases and certain phenotypic traits (2).