Screening fetal losses for monosomy X with a simple PCR-based procedure

Abstract

To screen for monosomy X in spontaneous fetal losses we explored a simple molecular strategy based on loss of heterozygosity at highly polymorphic X-linked loci. We developed a multiplex fluorescent procedure that allows the simultaneous amplification of five dinucleotide repeat polymorphisms in a large low-recombination region in the long arm of the X chromosome. Analysis was performed by computer-assisted laser densitometry. We did not find any instances of homozygosity at all five loci in 30 normal females tested, nor among 37 women whose typing data were retrieved from the Fondation Jean Dausset - CEPH genotype database. In addition, all cases of monosomy X previously diagnosed by conventional cytogenetics presented the anticipated loss of heterozygosity at all loci. We studied 19 spontaneously aborted female fetuses and we found four samples homozygous for the five loci (21%), in good agreement with the expected rate of monosomy X in first trimester spontaneous abortions. We conclude that the loci have high diversity and high efficiency in PCR-amplification and that our multiplex procedure constitutes a simple and useful molecular screening test for monosomy X in abortions and stillbirths.