[Trisomy 21. Report of 2 cases with unusual karyotypes].

We report two patients with trisomy 21 whose karyotypes revealed unusual translocations. In the first case there was a tandem translocation with two chromosomes 21 attached to the long arm of chromosome 10 (45,XX + tan(10:21;21). In the second case there was an inverted tandem translocation between two chromosomes 21 attached through their long arms (46,XY + dic(21q:21q). The clinical picture in both patients was not different from the usually found in trisomy 21. Since the parent's karyotypes were normal in both cases, it is assumed that both translocations arose "de novo". The need for karyotyping all cases of Down syndrome is emphasized.