Nuclear protein contents in peripheral blood mononuclear cells of trisomy 21 infants

The trisomy 21 (Ts21) or Down's syndrome (DS) phenotype is assumed to occur primarily by the expression/overexpression of some genes encoded by the extra chromosome 21. It has recently been shown by AgNOR staining that babies with Ts21 have more AgNOR area (more NOR proteins) and more RNA content in their peripheral blood mononuclear cells (PBMCs) than those of controls. The aim of this study was to test whether or not the nuclear proteins content of PBMCs from trisomy 21 babies/infants is higher than that of the controls.

For this purpose, flow cytometric measurement of the stained PBMC nuclei was used. Nuclei from PBMCs was isolated and stained with propidium iodide and fluorescein isothiocyanate (PI/FITC) for DNA and protein estimation, respectively.

Mean nuclear protein content of Ts21's (N = 30, mean age = 3.46 +/- 3.05 years old) PBMCs was found statistically higher than that of the controls (N = 33, mean age = 3.79 +/- 1.93 years old) (P = 0.005, nonparametric Mann-Whitney U test for two independent variables). This means that the average nuclear protein content of PBMC from Ts21 infants is higher than that of the controls. Furthermore, there is a moderate negative correlation between the ages of the studied DS patients and the protein content in the nuclei of their PBMCs (Linear regression analysis: P = 0.002, r = -0.55). This correlation is not found with controls (P = 0.186, r = -0.24).

We have concluded that average protein content of PBMCs' nuclei from DS infants is higher than that of the controls, decreasing significantly with age.