Evidence against the current hypothesis of "gene dosage effects" of trisomy 21: ets-2, encoded on chromosome 21" is not overexpressed in hearts of patients with Down Syndrome

Background: The major current concept for the pathogenesis of the Down Syndrome (DS) phenotype including congenital heart disease (CHD) is the so-called "gene dosage effect." According to this hypothesis, genes encoded by chromosome 21 at the "critical region" (which is thought to be crucial for the development of the DS phenotype) are overexpressed in the trisomic state, thus leading to an imbalance of genes as, e.g., the protooncogene ets-2, superoxide dismutase, etc. Methods: We studied heart biopsies obtained at surgery from 6 patients with DS and 7 patients with congenital heart disease. ets-2-mRNA steady state levels were determined by a competitive reverse transcription-polymerase chain reaction (RT-PCR) technique which allowed the determination of this gene at the attomol level. Results: ets-2 mRNA in total ventricular tissue of DS patients showed concentrations of 0.60 +/- 0.42 fg/10 ng total RNA (mean, +/- SD). When normalized versus the housekeeping gene betaactin to rule out general transcriptional changes in that disorder, the ratio of 0.56 +/- 0.28 (mean, +/- SD) was calculated, ets-2 mRNA in total ventricular tissue of patients with non-DS CHD showed concentrations of 0.45 +/- 0.22 fg/10 ng total RNA (mean, +/- SD) and ratios of 0.48 +/- 0.35 (mean, +/- SD). No differences could be found at the p < 0.05 level. Conclusion: No absolute quantification of a gene incriminated in the "gene dosage effect-hypothesis" was performed so far and the only approach to (semi-) quantitative determination of the ets-e gene using northern blotting was published on one individual DS sample only. This is the first report to clearly show that no overexpression of ets-2 can be found in heart of patients with DS, thus providing evidence against the current gene dosage effect-hypothesis. (C) 1999 Academic Press.