High maternal serum chorionic gonadotropin level in Downs' syndrome pregnancies is caused by elevation of both subunits messenger ribonucleic acid level in trophoblasts.

A unique product of human placenta is CG. Its concentration in maternal blood rises exponentially until 9-10 weeks' gestation, thereafter, it decreases to about 20% of the maximum, remaining constant from 16-17 until 40 weeks. High second-trimester maternal blood level indicates an increased risk for Downs' Syndrome (DS). This study's aim was to determine whether changes occur in the genetic expression of CG subunits in cultured trisomy-21 trophoblasts compared with various gestational age controls. Second-trimester trisomy-21 trophoblasts secrete 10 times more CG than gestational age-matched controls during the first day in culture: 878 (range, 235-2230) IU/g vs. 87 (range, 20-150) IU/g (P < 0.05). This high secretion closely resembles quantities secreted by first-trimester normal trophoblasts: 7500 (range, 3,850-10,000) IU/g. Both subunits' messenger RNA content are substantially increased, CG beta much more than CG alpha, although these genes are not located on chromosome 21. We conclude that at least one cause of high second-trimester maternal blood CG in DS pregnancies is a rise in alpha and beta CG messenger RNA levels in the trophoblast. We propose that at 12-14 weeks, when rapid decrease in maternal blood CG levels can be found, higher than normal values may indicate an increased risk for DS.

Down's syndrome as a model for the decisive role of maternal lineage in human evolution.

The study of human evolution and the mechanism of this process can be approached from physical anthropology, which examines phenotypic expression and molecular evolution, which investigates genotypic change. Alternatively, we suggest that human evolutional process can also be explained using present day examples of abberations in evolution. Thus, from both genotypic and phenotypic perspectives, we address the question of whether Down's syndrome is an instructive example to look into the decisive role of maternal lineage in human evolution.

Genetic imprinting in human evolution: the decisive role of maternal lineage.

The modern study of human evolution must take into account physical anthropology, which examines phenotypic expression, and molecular evolution, which examines genotypic change. Recent independent investigations have shown that the process of genetic imprinting, defined as parental-dependent transmission of genetic traits, plays a pivotal role in human evolution. We draw on data from various scientific disciplines to support the hypothesis that maternal lineage via preferential genetic contribution, plays a decisive role in this regard. This concept is of more than theoretical interest, in that, current human disease states can be better understood and studied in the context of loss of genetically-defined evolutionary advantage.

ABL and BCR genes are not imprinted in androgenetic and gynogenetic human tissues.

In the translocation leading to the formation of the Philadelphia chromosome, the hallmark of chronic myeloid leukemia (CML), the translocated chromosome 9 (ABL), is of paternal descent whereas chromosome 22 (BCR) is of maternal origin (1). To study possible imprinting of the human ABL and BCR genes, we used human tissues exclusively endowed with their maternally (benign teratoma) or paternally (complete hydatidiform mole) inherited chromosomes. Using the sensitive PCR technique followed by northern blotting, we demonstrate here that ABL and BCR are expressed to a similar extent in androgenetic and gynogenetic human tissues, thus suggesting that ABL and BCR genes are not imprinted in these human tissues.