| Modification Notes |
PLAC4 (placenta-specific 4), also known as D21S418E, is a 150 amino acid protein that is expressed in maternal plasma by placental syncytiotrophoblast and choriocarcinoma cells. PLAC4 is fetal derived, therefore it is specifically expressed during pregnancy and clears from maternal plasma within 24 hours after delivery. The PLAC4 gene is located on chromosome 21 and has four single nucleotide polymorphisms (SNPs) in its transcribed regions. This allows for PLAC4 to be a target gene in the noninvasive prenatal detection of trisomy 21 by allelic ratio analysis of placental expressed mRNA transcripts in maternal plasma. In a heterozygous fetus, both alleles of an SNP should be represented equally. An imbalance in allele frequency, giving a 2:1 ratio, suggests an additional copy of chromosome 21 and thus detection of trisomy 21. In addition, PLAC4 may be a useful target in the prenatal detection of Down syndrome. |
