Association frequency and silver staining of nucleolus organizing regions in hyperthyroid patients

The intensity of the silver staining of nucleolus organizing regions (NORs) and the frequency of chromosomal associations were studied before and after antithyroid treatment in seven and eight hyperthyroid patients, respectively. For one patient, the NOR staining was significantly more intense after treatment, while for another the opposite result was found. A higher stainability of chromosome 22 was observed after treatment in six of seven patients. The difference was significant for the group of patients considered as a whole but only for one patient considered separately. Chromosome 22 also showed an increased association frequency. Fro one patient, the number of large associations and the total number of associating chromosomes was also significantly increased after treatment. A decrease of associating chromosomes 14 and 21 such as was reported by Nilsson et al, (1975) after antithyroid treatment could not be found in our sample. The possible reason for this difference are discussed.