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.

Research Article MQS-PCR: a simple and quick multiplex PCR molecular method for human chromosomal sex determination in DNA samples

“…Since it depends on the polymorphism of the five loci tested, it does not provide incontrovertible evidence for or against the presence of a 45,X chromosomal sex when all five loci show a single peak, suggesting homozygosity. Indeed, application of Bayes" theorem allows us to calculate that given apparent homozygosity at all five loci, the probability of a first trimester spontaneously aborted female fetus having monosomy X is 98.4% (Pereira et al, 2000). Differently, the multiplex described here provides 100% sensitivity and specificity for the diagnosis of monosomy X.…”

“…Also, we have reported previously the use of a single-tube multiplex PCR set of five polymorphic microsatellites for the diagnosis of monosomy X in fetal losses (Pereira et al, 2000). Since it depends on the polymorphism of the five loci tested, it does not provide incontrovertible evidence for or against the presence of a 45,X chromosomal sex when all five loci show a single peak, suggesting homozygosity.…”