 Rare fragile sites can lead to genetic disease such as fragile X mental retardation syndrome, myotonic dystrophy, Friedrich’s ataxia, and Huntington’s disease, most of which are caused by expansion of repeats at the DNA, RNA, or protein level.Although, seemingly harmful, these common fragile sites are conserved all the way to yeast and bacteria.These ubiquitous sites are characterized by trinucleotide repeats, most commonly CGG, CAG, GAA, and GCN.