Abstract
We present a case previously described by Jenkins et al. (1983) as atypical Down syndrome (DS). The initial diagnosis was first made on the basis of phenotypic and cytogenetic data. This analysis was supported by studies of superoxide dismutase (SOD1) activity that maps to band 21q22.1. Results from phenotypic, chromosome banding and SOD1 studies suggested a karyotype of 46,XX,-12,+t(12pter to 12qter::21q21 to 21q22.?2). Using fluorescent in situ hybridization (FISH) for chromosome painting with DNA libraries derived from sorted human chromosomes to stain selectively the chromosomes No. 21 and No. 12, we demonstrate that the marker chromosome 12q+ has no chromosome 21 content but it is derived from chromosome 12.