Amber Burgess¹, Ellen Casey¹, Lorna Williams¹, David Francis¹, Vida Petrovic¹, Nicola Flowers¹, Mark Pertile^1,2, Sebastian Lunke¹ and Meg Wall¹

¹Victorian Clinical Genetics Services, Murdoch Children’s research Institute, Royal Children’s Hospital, Melbourne Victoria; ²Department of Paediatrics, Melbourne University, Melbourne, Victoria

Our understanding of constitutional chromosomal mosaicism continues to evolve as new sampling techniques and methods for testing are developed. Chromosomal testing of amniotic fluid and chorionic villus samples (CVS) has been the mainstay of prenatal diagnosis for decades (1970’s and 80’s respectively). The introduction of chromosomal microarray analysis (CMA), which is usually performed on uncultured cells, has been a game changer for testing of products of conception (POC) samples but has made the interpretation of results from uncultured amniotic fluid samples sometimes difficult. Genome-wide prenatal cell free DNA screening, along with direct DNA testing of POCs has further developed our understanding of early embryonic mosaicism. In the newborn period, testing of placental tissues from the pregnancy or blood or saliva from the baby are options for the investigation of confined placental and tissue limited constitutional mosaicism. In our laboratory we have performed extensive testing in pregnancies where there has been tissue limited mosaicism. The presentation will focus on when and where chromosomal mosaicism is detected to inform which tissue to test depending on the clinical indication.