Lack of specificity of DA/DAPI fluorescence.

Cytogenetic studies showed 47,XY, + mar in a developmentally retarded child with some features of Prader-Willi syndrome, and 46,XX in his mother. The marker chromosome showed a single subterminal primary constriction, bisatellites, and two C-bands. DA/DAPI staining showed two intense bands in the marker chromosome, which most likely was derived from chromosome 15. Intense DA/DAPI fluorescence was also found in one chromosome 13 in the child, and one 13 and one 10 in his mother. The present results confirm the reports of DA/DAPI heteromorphism in acrocentric chromosomes other than the 15, and demonstrate a pericentric DA/DAPI heteromorphism in chromosome 10.