Sporadic aneuploidy in PHA-stimulated lymphocytes of trisomies 21, 18, and 13.

Following the observation detected in a previous study that X chromosome monosomy in Turner's syndrome genotypes was associated with a sporadic loss and/or gain of other chromosomes, we studied here whether this instability is a consistent finding in constitutional autosomal trisomies. We used PHA-stimulated lymphocytes derived from 14 patients (10 patients with trisomy 21, 2 with trisomy 18, and 2 with trisomy 13). Fourteen healthy controls were compared. Fluorescence in situ hybridization, applied at interphase cells, was used to evaluate the level of aneuploidy for 3 randomly selected chromosomes (autosomes 8, 15, and 16) in each sample. For each tested chromosome, our results showed a significantly higher level of aneuploid cells in the samples from the patients than in those from controls, with no difference between the patient groups. The mean level of aneuploid cells (percentage) for all 3 tested autosomes was almost twice as high in the patient samples as in the control samples. The aneuploidy level was mainly due to monosomy, which was significantly higher in the samples from the patients than in those from controls for each one of the tested chromosomes, with no difference between the patient groups. The mean level of monosomic cells (percentage) for all 3 tested chromosomes was almost twice as high in the patient samples as in the control samples. Our study shows that various constitutional autosomal trisomies are associated with an increased frequency of non-chromosome specific aneuploidy and is a continuation of the previous study documenting sporadic aneuploidy in Turner's sample cells. It is possible that primary aneuploid cells destabilize their own genome resulting in variable aneuploidy of other chromosomes. It is also possible that one or several common factor(s) is/are involved in both constitutional and sporadic aneuploidy.