Spontaneous rescue of a FMR1 repeat expansion and review of deletions in the FMR1 non-coding region.

Fragile X syndrome (FXS) is caused by CGG-repeat expansion in the 5' UTR of FMR1 of >200 repeats. Rarely, FXS is caused by deletions; however, it is not clear whether deletions including only the non-coding region of FMR1 are pathogenic. We report a deletion in the 5' UTR of FMR1 in an unaffected male infant and review 12 reported deletions involving only the non-coding region of FMR1.