When suspected monosomy X turns out to be more

Confirming sex chromosome abnormalities and predicting clinical implications can be trickier than you think. Here’s one case series that proves this point.

Noninvasive cell-free DNA (cfDNA) screening is designed to tell you fetal risk for certain aneuploidies, and can include information about sex chromosomes.

We found a series of cases where the fetus was suspected to have monosomy X and connected with the providers to learn more about how follow-up to these results can get complicated.

What did we find?

  • 3 cases with cfDNA screening results indicative of monosomy X were found to have an isodicentric Y chromosome on follow-up diagnostic testing.1
  • This data further supports cases published in the literature showing variable phenotypes in patients’ mosaic for isodicentric Y and monosomy X.1
  • Pre- and post-test counseling is important to ensure patients understand the limitations of cfDNA screening and the importance of diagnostic follow-up.

Isodicentric Y Case Series Thumbnail


This research was presented at the 2017 National Society of Genetic Counselors (NSGC) Annual Meeting.

Download the poster

Tessa Niemchak - Progenity MSL

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  1. Owens et al. Isodicentric Y chromosome karyotypes identified following positive prenatal noninvasive cell-free DNA screening results: A case series. Poster presented at NSGC 2017. Columbus, Ohio.