Double trisomy as a mosaic. Case history (48, XYY, + 21/47,XY, +21) and survey of the literature of mixed autosomal-gonosomal trisomies.

The case of a boy is reported showing the typical symptoms of Down's syndrome, in whom the chromosome analysis revealed a mosaic karyotype: 50% 48,XYY,+21/50% 47,XY,+21. Findings of 92 cases from the literature are summarized to show the frequencies of double gonosome-autosome aneuploidies compared with single trisomies. Referring to the different chromosomes involved, the aneuploid cell formation, the frequencies of combinations, as well as the tendency to mosaic formation are analyzed. The age of parents at the time of birth and the life expectancy are described as well as the clinical symptoms. Theories concerning the origin of double aneuploidies are discussed.