Two chromosome fragments in a child with Down's syndrome and transient chromosome aberrations in the mother.

We wish to report a trisomy 21 child with two supernumerary fragments, whose mother had possibly related transient chromosome aberrations. The proband was an 8-year-old boy with typical features of Down's syndrome. The lymphocyte chromosomes studied at the ages of 3-5 months and 8 years showed a mosaic karyotype with both cell lines with trisomy 21 and one line (52% of the cells) with two additional fragments (fig 1). The fragments were different sizes with the smaller one resembling the so-called minute chromosomes. The origin of the markers remains unknown despite staining with different methods (standard Giemsa, G, Q, C, and N bands and Harlequin staining). The larger fragment showed some size variation from cell to cell, suggesting ring formation. The fragments had no satellites and were C and N band negative (fig lb, c). Harlequin staining revealed that the smaller one replicated earlier than the larger one (fig le). Karyotypes of both parents were normal. In 60 out of 200 cells of the mother, however, major chromosome aberrations such as dicentric and ring chromosomes plus acentric fragments were seen (fig 2). Eight years later no such changes were seen in 200 cells studied. The presence of an additional fragment is quite rare and to our knowledge the presence of two dissimilar minute marker chromosomes has not been reported before. The origin of the marker chromosomes could not