THE ORIGIN OF MOSAIC DOWN SYNDROME - 4 CASES WITH CHROMOSOME MARKERS

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  • 1 January 1984
    • journal article
    • research article
    • Vol. 36  (1) , 123-130
Abstract
Four children, a girl and 3 boys, with diploid/trisomic mosaic Down syndrome were studied for the mechanism of origin of mosaics, using Q- and R-banding heteromorphisms as markers. Three mosaic subjects started as a trisomic zygote followed by the loss of a chromosome 21 at an early mitotic division. Of these, 1 resulted from a maternal 1st-meiotic error, another resulted from a paternal 1st-meiotic event, and the 3rd originated from a 1st-meiotic error in either parent. The remaining subject could have resulted from either a diploid or a trisomic zygote. These findings, together with a higher proportion of trisomic cells in skin fibroblasts than in peripheral blood lymphocytes in the 2 patients studied, suggest that the extra chromosome 21 in mosaic Down syndrome patients usually has a meiotic origin. At least 2, possibly 3, of the diploid cell lines in these mosaics consisted of uniparental chromosomes 21, namely, both the homologous members were derived from a parent.