Finding FMR1 mosaicism in Fragile X syndrome

Thaís Fernandez Gonçalves, Jussara Mendonça Dos Santos, Andressa Pereira Gonçalves, Flora Tassone, Guadalupe Mendoza-Morales, Márcia Gonçalves Ribeiro, Evelyn Kahn, Raquel Boy, Márcia Mattos Gonçalves Pimentel, Cíntia Barros Santos-Rebouças

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


OBJECTIVE: Almost all patients with Fragile X Syndrome (FXS) exhibit a CGG repeat expansion (full mutation) in the Fragile Mental Retardation 1 gene (FMR1). Here, the authors report five unrelated males with FXS harboring a somatic full mutation/deletion mosaicism. METHODS: Mutational profiles were only elucidated by using a combination of molecular approaches (CGG-based PCR, Sanger sequencing, MS-MLPA, Southern blot and mPCR).RESULTS: Four patients exhibited small deletions encompassing the CGG repeats tract and flanking regions, whereas the remaining had a larger deletion comprising at least exon 1 and part of intron 1 of FMR1 gene. The presence of a 2-3 base pairs microhomology in proximal and distal non-recurrent breakpoints without scars supports the involvement of microhomology mediated induced repair (MMBIR) mechanism in three small deletions. CONCLUSION: The authors data highlights the importance of using different research methods to elucidate atypical FXS mutational profiles, which are clinically undistinguishable and may have been underestimated.

Original languageEnglish (US)
Pages (from-to)501-507
Number of pages7
JournalExpert Review of Molecular Diagnostics
Issue number4
StatePublished - Apr 2 2016


  • copy number variation
  • deletion
  • FMR1 gene
  • Fragile X syndrome
  • mosaicism

ASJC Scopus subject areas

  • Pathology and Forensic Medicine
  • Molecular Medicine
  • Molecular Biology
  • Genetics


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