Double aneuploidy with Down's-Klinefelter's syndrome.

The occurrence of double aneuploidy, ie, the existence of two chromosomal abnormalities in the same individual, is a relatively rare phenomenon. A 1-year-old boy with Down's syndrome resulting from de novo mosaic 21 trisomy with an additional X in the karyotype: 47,XXY/48,XXY,+21 (4%/96%) is reported. Besides the typical features of Down's syndrome, the patient did not have the commonly associated conditions (recurrent respiratory tract infections, congenital heart disease, thyroid or digestive tract problems). A molecular cytogenetic method with biotin-labeled probe D13Z1/D21Z1 was used to confirm the diagnosis and to clarify the status of Down's syndrome mosaicism which explained the milder stigmata of Down's syndrome in this case. The coexistence of Klinefelter's syndrome (47,XXY) also may have contributed to the development of normal height and micropenis in this patient. To our knowledge, this is the first case of Down's syndrome together with Klinefelter's syndrome in Taiwan.