Molecular Mechanisms of TRS Instability

Abstract
Microsatellites, stretches of short, tandemly repeated motifs of one to six nucleotides are very unstable and display very high polymorphism among individuals. 1 , 2 , 3 , 4 Of these repeats, a special class of microsatellites, trinucleotide repeat sequences (TRS) are involved in human neurodegenerative diseases. 5 , 6 To date, several neurological or neuromuscular hereditary human disorders—also called mental retardation diseases—have been linked to the genetic instability of the TRS. Diseases including myotonic dystrophy, Huntington’s disease, Kennedy’s disease, fragile X syndrome, spinocerebellar ataxias or Friedreich’s ataxia result from expansion of trinucleotide sequences such as (CTG/CAG)n, (CGG/CCG)n, or (GAA/TTC)n present in human genome.7