Prenatal diagnosis of fragile x syndrome: (cgg)n expansion and methylation of chorionic villus samples

Sergi Castellví‐Bel, Montserrat Milà, Anna Soler, Ana Carrió, Aurora Sánchez, Margarita Villa, M. Dolores Jiménez, Xavier P. Estivill

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18 Citations (Scopus)


Fragile X syndrome is the most common form of inherited mental retardation, due to an expansion of the (CGG)n trinucleotide repeat in the FMR‐1 gene and hypermethylation of its 5′ upstream CpG island. Two major problems remain to be resolved for fragile X prenatal diagnosis: the abnormal methylation patterns of chorionic villus samples (CVS) and the inability to predict the mental status of females with the full mutation. We present here the results of ten prenatal diagnoses of fragile X syndrome using Southern blotting and polymerase chain reaction (PCR) amplification, and the analysis of 50 further CVS to test the methylation status of the CpG island of the FMR‐1 gene. In the ten ‘at‐risk’ CVS, eight normal (five males and three females) and two affected male fetuses were detected. Absence of methylation in the CVS was observed in two cases, which was not found upon subsequent examination of the newborn or of fetal tissues. In the 50 CVS not ‘at risk’ for fragile X syndrome, abnormal fragment patterns for probe StB12.3 were detected in 32 per cent for female and 24 per cent for male fetuses. This abnormal pattern could be due to absent or partial methylation of the CpG island of the FMR‐1 gene in chorionic villus tissues.

Original languageEnglish
Pages (from-to)801-807
Number of pages7
JournalPrenatal Diagnosis
Issue number9
Publication statusPublished - 1995
Externally publishedYes



  • chorionic villus samples
  • DNA methylation
  • FMR‐1 gene
  • fragile X syndrome
  • prenatal diagnosis

ASJC Scopus subject areas

  • Obstetrics and Gynaecology
  • Genetics(clinical)

Cite this

Castellví‐Bel, S., Milà, M., Soler, A., Carrió, A., Sánchez, A., Villa, M., Jiménez, M. D., & Estivill, X. P. (1995). Prenatal diagnosis of fragile x syndrome: (cgg)n expansion and methylation of chorionic villus samples. Prenatal Diagnosis, 15(9), 801-807.