American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

If 50% of cells from an amniotic flask show 92,XXYY and the other 50% show 46,XY, what does this likely indicate?

1. Trisomy

2. Pseudomosaicism

3. Chromosomal aberration

4. Normal variation

The correct answer is: Pseudomosaicism

The observation of 50% of cells showing a karyotype of 92,XXYY and the other 50% showing 46,XY indicates a scenario known as pseudomosaicism. In pseudomosaicism, two different cell lines are present in a sample, but they do not arise from a true mosaic condition where both cell lines coexist due to an error in mitosis or other developmental events after fertilization. In this case, the 92,XXYY karyotype suggests a tetraploid condition, while the 46,XY represents a normal male karyotype. The fact that both cell lines are present in equal proportions implies that they likely originated from different sources rather than the same individual cells. This can happen in amniotic fluid where some cells picked up can originate from the surrounding tissues along with the fetal cells, leading to a mixed cell population. Thus, the finding of two distinct and balanced karyotypes within the sample supports the interpretation of pseudomosaicism, rather than indicating a true chromosomal abnormality or a variation typically associated with genetic conditions.