Prenatal diagnosis of a case with complete and uniform tetrasomy 12p by the utility of noninvasive prenatal testing

Purpose To report a rare type of Pallister-Killian syndrome (PKS) diagnosed prenatally by the utility of non-invasive prenatal testing (NIPT). Methods NIPT was performed in the first trimester. Conventional karyotyping and chromosomal microarray analysis (CMA) were performed on the amniotic samples in the second trimester. Copy number variation sequencing (CNV-seq) was used for the validation of fetal skin and the placental tissue after pregnancy termination. Results NIPT results showed increased signal from chromosome 12p. Subsequent prenatal diagnostic testing by karyotype revealed 47, XY, +i (12p), and CMA displayed four copies of 12p: 12p13.33-12p11.1(173786_34835641) × 4. The CNV-seq results of the fetal skin and the fetal side of placenta showed four copies of 12p13.33-p11 and an estimated chimeric duplication of 34.08 Mb (chimerism ratio: 10%) in 12 p13.33-p11, respectively. However, no abnormality was detected by CNV-seq at the maternal side of placenta. Conclusions Our findings suggest that a positive signal from chromosome 12p on NIPT should raise suspicion for PKS. With the wide application of NIPT, the true positive of incidental finding is expected to increase.