Mosaicism for an FMR1 gene deletion in a fragile X female

Hongxin Fan, Jessica K. Booker, Shawn E. McCandless, Vandana Shashi, Alison Fleming, Rosann A. Farber

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Most cases of fragile X syndrome result from expansion of CGG repeats in the FMR1 gene; deletions and point mutations of FMR1 are much less common. Mosaicism for an FMR1 full mutation with a deletion or with a normal allele has been reported in fragile X males. Here we report on a fragile X female who is mosaic for an FMR1 full mutation and an intragenic deletion. The patient is a 4-year-old girl with developmental delay, autistic-like behaviors, and significant speech and language abnormalities. Southern blotting demonstrated the presence of a methylated full mutation, a normal allele in methylated and unmethylated forms, and an additional fragment smaller than the normal methylated allele. This result indicates that the patient is mosaic for a full mutation and a deletion, in the presence of a normal allele. By DNA sequence analysis, we mapped the 5′ breakpoint 63/65 bp upstream from the CGG repeat region and the 3′ breakpoint 86/88 bp downstream of the CGG repeats within the FMR1 gene. The deletion removed 210 bp, including the entire CGG repeat region. The full mutation was inherited from a premutation in the patient's mother. The deletion, which remained methylated at the Eag I and Nru I sites, was probably derived from the full mutation allele. Mosaicism of this type is rare in females with a fragile X mutation but should be kept in mind in the interpretation of Southern blots.

Original languageEnglish (US)
Pages (from-to)214-217
Number of pages4
JournalAmerican Journal of Medical Genetics
Volume136 A
Issue number2
StatePublished - Jul 15 2005


  • Deletion
  • FMR1 gene
  • Fragile X syndrome
  • Mosaicism
  • Repeat-expansion disorder

ASJC Scopus subject areas

  • Genetics(clinical)
  • Genetics


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