Characterization of the full fragile X syndrome mutation in fetal gametes

Nat Genet. 1997 Feb;15(2):165-9. doi: 10.1038/ng0297-165.


Fragile X syndrome results from the expansion of the CGG repeat in the FMR1 gene. Expansion has been suggested to be a postzygotic event with the germline protected. From an analysis of intact ovaries of full mutation fetuses, we now show that only full expansion alleles can be detected in oocytes (but in the unmethylated state). Similarly, the testes of a 13-week full mutation fetus show no evidence of premutations while a 17-week full mutation fetus exhibits some germ cells with attributes of premutations. These data discount the hypothesis that the germline is protected from full expansion and suggest full mutation contraction in the immature testis. Thus, full expansion may already exist in the maternal oocyte, or postzygotic expansion, if it occurs, arises quite early in development prior to germline segregation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • DNA Methylation
  • DNA Mutational Analysis
  • Female
  • Fetal Diseases / genetics*
  • Fetal Diseases / pathology
  • Fetal Proteins / genetics*
  • Fragile X Mental Retardation Protein
  • Fragile X Syndrome / embryology
  • Fragile X Syndrome / genetics*
  • Genomic Imprinting*
  • Gestational Age
  • Humans
  • Male
  • Models, Genetic
  • Nerve Tissue Proteins / genetics*
  • Oocytes / chemistry*
  • Ovary / embryology
  • RNA-Binding Proteins*
  • Spermatozoa / chemistry*
  • Testis / embryology
  • Trinucleotide Repeats*
  • X Chromosome / genetics*


  • FMR1 protein, human
  • Fetal Proteins
  • Nerve Tissue Proteins
  • RNA-Binding Proteins
  • Fragile X Mental Retardation Protein