[Frequency of mixoploidy in 85 index cases with Down syndrome]

A lymphocyte chromosome analysis was done in 85 cases of trisomy 21 Down syndrome, the objective being the identification of the frequency of mosaicism. In each case an attempt was made to analyse at least 100 metaphases. Sixteen cases of mixoploidy were found (18.8%) with two or more cellular lines. These findings are discussed in relation with the frequency of the association between Down's syndrome and other aneuploidies, the frequency of the diploid/trisomy 21 mosaicism, and the possible origin of the latter.