The prevalence of the FMR1 and FMR2 mutations among preschool children with language delay

J Pediatr. 1998 May;132(5):795-801. doi: 10.1016/s0022-3476(98)70306-3.


We examined the prevalence of the fragile X mental retardation (FMR1) full mutation and fragile X E mutation (FMR2) among preschoolers evaluated for language delay. A total of 534 preschoolers recruited from a Developmental Pediatric or Speech and Language Disorders clinic were tested with Southern blot and polymerase chain reaction DNA analyses; 3 were found to have the FMR1 full mutation. None of the 534 children tested positive for the FMR2 full mutation; however, 3 children had unusually small FMR2 alleles suggestive of FMR2 deletions. Screening for fragile X among language-delayed preschoolers is warranted, particularly when there is a family history of mental retardation, but regardless of sex or the presence of behavioral or physical features associated with the fragile X phenotype. The potential benefit of screening for FMR2 alterations is an unexpected implication of the study and is worthy of continued exploration.

Publication types

  • Case Reports
  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Blotting, Southern
  • Child, Preschool
  • Female
  • Fragile X Syndrome / complications*
  • Fragile X Syndrome / diagnosis
  • Fragile X Syndrome / epidemiology
  • Fragile X Syndrome / genetics*
  • Humans
  • Infant
  • Language Development Disorders / etiology*
  • Language Development Disorders / genetics
  • Male
  • Mutation
  • Phenotype
  • Polymerase Chain Reaction
  • Prevalence
  • Trinucleotide Repeat Expansion