A search on karyotypic mosaicism in mongoloid patients and their parents

The frequency of chromosomal mosaicism among patients with clinical diagnosis of mongolism was determined. Among 50 patients with at least 32 cells studied, 2 (or 4%) were found to be mosaics of the 46/47, +G type. Among 350 patients with at least 5 cells studied, 2 (or 0.57%) 46/47, +G mosaic cases were detected. Taking in account the probability of detecting mosaicism when 5 cells are analysed, a frequency of 0.58% of mosaic cases was estimated for this sample. The mosaic patients were submitted to repeated cytogenetic examination. One of these cases showed significant differences between the frequencies of normal cells, but a linear regression analysis showed that there was no correlation between the frequency of these cells and the patient's age. Clinically, the mosaic patients showed no consistent differences in the severity of the syndrome when compared to mongoloids without mosaicism. A frequency of 16 translocation cases (4%) was found in the total number of mongoloid patients studied. In a sample of 190 parents of regular trisomy-21 children no mosaicism was found in the blood. Also no significant differences were observed between the frequencies of aneuploid, hyperdiploid or hypodiploid cells and those obtained by other authors in the general population.