Flow cytometric comparison of RNA content in peripheral blood mononuclear cells of Down syndrome patients and control individuals.

OBJECTIVE: Trisomy 21 or Down syndrome (DS) is the most common genetic cause of mental retardation associated with the immunologic and other known defects. Extra chromosome 21 of DS patients contains an average of 40 extra copies of rRNA genes and the in vivo regulation of these genes' activity is not known. Because over 80% of total cellular RNA is rRNA, the measurement of total cellular RNA provides information on rRNA content. The aim of this work was to determine whether or not the additional chromosome 21 causes any increase in total cellular RNA content in mononuclear cells from peripheral blood (PBMNCs) of these patients and whether or not this content is modified with age.
METHOD: PBMNCs of 48 patients with DS and 48 healthy controls were studied. RNA content of isolated PBMNCs was evaluated by flow cytometric measurements.
RESULTS: Average RNA content of younger DS patients' cells was significantly higher than that of healthy controls (P=0.003). Furthermore, the RNA content decreased significantly with increasing age of DS patients (r=-0.377, P=0.008) in the range of 0-26 year old, whereas no significant relationship was found between age and PBMNCs' RNA content of healthy controls in the same range of ages.
CONCLUSION: RNA content of PBMNCs from DS patients decreases rapidly with age. This is the first work on the age-dependent decrease of the RNA content in PBMNCs of DS patients. Copyright (c) 2005 Wiley-Liss, Inc.