Congenital anomalies and developmental delay in a boy with double chromosome 6 derived supernumerary marker.

The frequency of small supernumerary marker chromosomes has been estimated to approximately 0.45 per 1000 newborns. They are usually seen as single marker chromosomes in a mosaic state. Two cytogenetically identical markers have been observed only occasionally. We report on a boy, with congenital heart defect, neonatal hypotonia, hypogenitalism, delayed psychomotor development and mild dysmorphic facial features. The GTG karyotype performed on peripheral blood lymphocytes revealed a mosaic male karyotype with three cell lines. One cell line had a normal karyotype. In the other two either single or double chromosome 6 derived supernumerary markers were present, leading to partial trisomy or partial tetrasomy of chromosome 6, respectively.