Over 20 unstable microsatellite repeats consisting of repeats of 3–5 nucleotides have been linked to neurological diseases, including the CGG repeats in the FMR1 gene for fragile X syndrome, the CAG repeats in the androgen receptor for Kennedy's disease, the CAG repeats in the huntingtin gene for Huntington's disease (HD), the CTG repeats in the DMPK gene for myotonic dystrophy type 1, the CCTG repeats in the ZNF9 gene for myotonic dystrophy type 2, and the ATTCT repeats in the ATXN10 gene for spinocerebellar ataxia type 10 [62] . Here, HTT is linked to fragile X syndrome.