High levels of maternal serum human chorionic gonadotropin in Down syndrome pregnancies: the possible role of a transcription factor on chromosome 21.

Increased levels of human chorionic gonadotropin (hCG) are used as markers for Down syndrome (DS) screening of low-risk populations. The pathophysiology for increased hCG levels remains unknown. In general, hCG synthesis is limited by the rate of beta-chain formation. In the placenta, 2 of a total of 6 hCG beta-genes are expressed. We hypothesized that in DS, a transcriptional factor may upregulate beta-chain transcription by interacting with the beta5-promoter. Primary cell cultures of skin fibroblasts from both normal and DS midtrimester fetuses were established and transfected with the beta5-promoter linked to the chloramphenicol-acetyl-transferase reporter gene. The chloramphenicol-acetyl-transferase activity was measured. Three of six DS-derived cell cultures showed a three-fold increase in acetylation. The increase in hCG promoter activity in DS-derived fibroblasts suggests a possible role for a transcriptional factor located on the human chromosome 21 by either directly or indirectly interacting with the beta5-promoter.