Use of chromosome painting for marker chromosome identification in two children with congenital disorders.

Identification of supernumerary de novo marker chromosomes was considered up to now as difficult and sometimes impossible with classical cytogenetical banding methods. The determination of their chromosomal origin is now easier with fluorescent in situ hybridisation techniques and enables an exact correlation between chromosomal aberration and phenotypic features to be established. The authors describe the use of chromosome painting with chromosome 13 and 18 Whole library DNA probe for identification of supernumerary markers in tow patients with congenital disorders. Cytogenetic examination in the first cave revealed a mosaicism with a ring chromosome 13 but clinical findings were different from the classical "ring 13 syndrome', and chromosome painting revealed in an extra--dicentric 13 chromosome (mos : 47, XX, -13, +r (13) +dic (13) / 46, XX, r (13) / 45, XX, -13 / 48, XX, -13, +r (13), (12) dic (13) / 47, XX, -13, + (2) r (13), R-banding pattern on prometaphases and chromosome painting in the second case confirmed the marker to be a 18 p isochromosome (47, XX, +i (18p)). The feasibility and the usefulness of chromosome painting in ascertainment of the possible genetic significance of markers is discussed.