I. Papoulidis, M. Kontodiou, M. Tzimina, I. Saitis, A.B. Hamid, E. Klein, N. Kosyakova, U. Kordaß, J. Kunz, E. Siomou, P. Nicolaides, S. Orru, L. Thomaidis, T. Liehr, M.B. Petersen, E. Manolakos

• 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.