Fragile X syndrome
In unaffected individuals, the FMR1 gene contains 5–44 repeats of the CGG codon, most commonly 29 or 30 repeats. Between 45 and 54 repeats is considered a "grey zone". Between 55 and 200 repeats in length is described as a premutation allele. Individuals with fragile X syndrome have a full mutation of the FMR1 allele, with over 200 repeats of the CGG codon.