Fragile X males with unmethylated, full mutation trinucleotide repeat expansions have elevated levels of FMR1 messenger RNA

Flora Tassone, Randi J Hagerman, Danuta Z. Loesch, Ave Lachiewicz, Annette K. Taylor, Paul J Hagerman

Research output: Contribution to journalArticle

117 Scopus citations

Abstract

Fragile X syndrome normally arises as a consequence of large expansions (n >200) of a (CGG)(n) trinucleotide repeat in the promoter region of the FMR1 gene. The clinical phenotype is thought to result from hypermethylation of the repeat and adjacent upstream elements, with consequent down-regulation of transcription (transcriptional silencing). However, the relationship between repeat expansion and transcription has not been defined in the full mutation range. Using the method of quantitative (fluorescence) reverse transcriptase polymerase chain reaction, we demonstrated previously that FMR1 mRNA levels are substantially elevated in premutation (55 ≤ n < 200) male carriers. In the current work, we report that in fragile X males with unmethylated alleles in the full mutation range (n > 200), FMR1 mRNA levels remain significantly elevated (mean 3.5-fold elevation; P = 6.7 x 10-3) relative to normal controls, even for alleles exceeding 300 repeats. This conclusion is independent of any assumption regarding the transcriptional activity of methylated alleles. However, if it were assumed that all methylated alleles were transcriptionally silent, the FMR1 mRNA levels for cells with unmethylated alleles would be even higher (mean 4.5-fold elevation; P = 2.1 x 10-4). These observations show that the full-mutation CGG expansion per se is not a strong impediment to transcription and that the apparent up-regulation of the FMR1 locus remains active in at least some cells with full-mutation alleles. (C) 2000 Wiley-Liss, Inc.

Original languageEnglish (US)
Pages (from-to)232-236
Number of pages5
JournalAmerican Journal of Medical Genetics
Volume94
Issue number3
DOIs
StatePublished - Sep 18 2000
Externally publishedYes

Keywords

  • Dynamic mutations
  • Gene silencing
  • Genetic anticipation
  • Reverse transcriptase polymerase chain reaction
  • Transcription

ASJC Scopus subject areas

  • Genetics(clinical)

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