Condensed chromatin surface and NORs surface enhancement in mitogen-stimulated lymphocytes of Down syndrome patients

Mitogen-stimulated lymphocytes of 20 Down syndrome (DS) patients with regul ar trisomy 21 contain more condensed chromatin surface (11.28 +/- 2.64% of the total nuclear surface: mean SD) and more nucleolus organiser regions su rface (13.21 +/- 3.45 %) than that of 12 healthy controls: (8.84 +/- 2.23 a nd 9.12 +/- 2.33 %, reciprocally). The source of this peculiarity has been investigated. A computer program was designed for the planimetric measureme nt of the condensed chromatin surface (CCs)/ total nuclear surface(TNs) and the nucleolus organiser regions surface (NORss) /TNs proportions in interp hase nuclei. CCs/TNs and NORss/TNs of 100 maximally activated nuclei (MANS) were measured for each patient and control case. The difference was found highly significant (P < 0.01). Nuclei with a diameter of greater than or eq ual to 17 mum measured on the slide (in flattened state) were considered as maximally activated nuclei (MANS). NORss/TNs enhancement and fluorescent i n situ hybridisation (FISH) studies in MANS of DS patients indicate that th is phenomenon is due to the over-expression (or lack of downregulative mech anism) of NORs (rDNA) to some extent, including the NOR of the supernumerar y chromosome 21. No statistical difference was observed between 12 healthy controls and 5 Robertsonian translocation type of DS Patients (where the tw o involved NORs are missing) when the two parameters were considered. (C) 2 001 Editions scientifiques et medicales Elsevier SAS.