Detection of Fetal-derived Paternally Inherited X-Chromosome Polymorphisms in Maternal Plasma

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Abstract
The recent demonstration of the presence of cell-free fetal DNA in the plasma and serum of pregnant women opens up new possibilities for noninvasive prenatal diagnosis ( 1)( 2)( 3)( 4)( 5). However, many published reports have used Y-chromosomal sequences that are present in a male fetus as a marker ( 1)( 6)( 7), an approach that is not applicable to the 50% of pregnancies that involve a female fetus. A marker allowing the positive identification of DNA from a female fetus in maternal plasma would be useful for the investigation of sex-linked genetic disorders and for the extension of studies on pathologies involving fetal DNA abnormalities ( 7)( 8) to pregnancies involving female fetuses. We reason that because the female fetus would have inherited a paternally derived copy of the X-chromosome, short tandem repeat (STR) polymorphisms on this chromosome could potentially be used as a fetus-specific marker for female fetal DNA. In this study, we tested this hypothesis using a panel of STRs on the X-chromosome.