PLAC4 (placenta-specific protein 4), was initially discovered as a gene whose mRNA was expressed in placental syncytiotrophoblast and choriocarcinoma cells. While the function of PLAC4 is currently unclear, its gene is known to be located on chromosome 21q22.3. Due to the PLAC4 gene location on chromosome 21 and the release of its mRNA transcripts into maternal bloodstream from the placenta, it has been proposed to be a useful marker noninvasive prenatal chromosome 21 aneuploidy detection, although other reports suggests that PLAC4 mRNA levels are not altered in the maternal circulation of pregnancies with trisomy 21.