Familial X centromere variant resulting in false‐positive prenatal diagnosis of monosomy X by interphase FISH

Interphase fluorescent in situ hybridization (FISH) analysis performed on uncultured amniotic fluid cells from a female fetus revealed a single signal using an X chromosome alpha‐satellite probe, and the absence of any signal using a Y chromosome alpha‐satellite probe. This result was initially interpreted as monosomy for the X chromosome in the fetus. Subsequent chromosome analysis from the cultured amniotic fluid cells showed two apparently normal X chromosomes. FISH using the X alpha‐satellite probe on metaphase spreads revealed hybridization to both X chromosomes, although one signal was markedly reduced compared to the other. The same hybridization pattern was observed in the mother of the fetus. This is the first report of a rare familial X centromere variant resulting in a false‐positive diagnosis of monosomy X by interphase FISH analysis for prenatal diagnosis. Copyright © 2001 John Wiley & Sons, Ltd.