Selective dual testing is expected to achieve a serious beneficial economical outcome and reduce parental anxiety produced by ambiguous cytogenetic findings. However, the percentage of 0.1% undetected clinically significant abnormalities cannot be ignored. A suggestion would include the offering of a choice to the pregnant women, undergoing prenatal screening, by informing them about different approaches and various complications.

Tetrasomy 9p is a rare chromosomal syndrome and about 30% of known cases exhibit mosaicism. Approximately 50 of the reported cases with tetrasomy 9p mosaicism show a characteristic facial appearance, growth failure, and developmental delay. However, 3 patients with mosaicism for isochromosome 9p and a normal phenotype have also been reported. We report 2 additional cases of clinically normal young females with tetrasomy 9p mosaicism, one of whom also exhibited X chromosome aneuploidy mosaicism leading to an overall of 6 different cell lines. STR analysis performed on this complex mosaic case indicated that the extra isochromosome was of maternal origin while the X chromosome aneuploidy was of paternal origin, indicating a postzygotic event.