Among full autosomal trisomies, only trisomies of chromosome 21 (Down syndrome), 
18 (Edwards syndrome) and 13 (Patau syndrome) are compatible with postnatal 
survival. But the mechanisms, how a supernumerary chromosome disrupts the normal 
development and causes specific phenotypes, are still not fully explained. As an 
alternative to gene dosage effect due to the trisomic chromosome a genome-wide 
transcriptional dysregulation has been postulated. The aim of this study was to 
define the transcriptional changes in trisomy 13, 18, and 21 during early fetal 
development in order to obtain more insights into the molecular etiopathology of 
aneuploidy. Using oligonucleotide microarrays, we analyzed whole genome 
expression profiles in cultured amniocytes (AC) and chorionic villus cells (CV) 
from pregnancies with a normal karyotype and with trisomies of human chromosomes 
13, 18 and 21. We observed a low to moderate up-regulation for a subset of genes 
of the trisomic chromosomes. Transcriptional levels of most of the genes on the 
supernumerary chromosome appeared similar to the respective chromosomal pair in 
normal karyotypes. A subset of chromosome 21 genes including the DSCR1 gene 
involved in fetal heart development was consistently up-regulated in different 
prenatal tissues (AC, CV) of trisomy 21 fetuses whereas only minor changes were 
found for genes of all other chromosomes. In contrast, in trisomy 18 vigorous 
downstream transcriptional changes were found. Global transcriptome analysis for 
autosomal trisomies 13, 18, and 21 supported a combination of the two major 
hypotheses.