Satellite associations and NOR staining in mitoses of trisomy 21 mosaicism

The pattern of acrocentric chromosomes was studied in 190 normal and 190 trisomic cells from a patient with trisomy 21 mosaicism. No significant differences were observed in the total numbers of associations, the numbers of mitoses with one, two, or three associations, or the numbers of associations in which more than two acrocentric chromosomes were involved. Nor was the total number of associating acrocentric chromosomes significantly different in the two cell types. The no. 21 chromosomes, however, associated significantly more often in the trisomic cells, while all other acrocentrics showed a somewhat decreased association tendency. The NORs of 20 normal and 20 trisomic cells were silver-stained. One of the three chromosomes 21 was only moderately stained, and one chromosome 14 was less well stained than in the normal cells. This difference was significant according to our estimation of the staining intensity. Since the results do not reflect differences between patients or techniques, they strongly suggest that there are compensatory relationships of gene dosage between the NORs of different types of acrocentric chromosomes.