Identification of de novo chromosomal markers and derivatives by spectral karyotyping

Despite major advances in molecular cytogenetics during the past decade and the important diagnostic role that fluorescence in situ hybridization (FIS H) plays in the characterization of chromosomal abnormalities, the usefulne ss of this technique remains limited by the number of spectrally distinguis hable fluorochromes or fluorochrome combinations. Overcoming this major lim itation would allow one to use FISH to screen the whole human genome for In troduction chromosomal aberrations which, until recently, was possible only through conventional karyotyping. A recently described molecular cytogenet ics technology, 24-color FISH using spectral karyotyping (SKY), permits the simultaneous visualization of all human chromosomes in 24 different colors . Most chromosomal aberrations detected during cytogenetic evaluation can b e resolved using routine cytogenetic techniques alone or in combination wit h single- or dual-color FISH. However, some cases remain unresolved, in par ticular de novo supernumerary marker chromosomes and de novo unbalanced str uctural rearrangements. These findings cause particular diagnostic and coun seling concerns when detected during prenatal diagnosis. The purpose of thi s report is to demonstrate the application of SKY in the characterization o f these de novo structural chromosomal abnormalities. Eight cases are descr ibed in this report. SKY has considerable diagnostic applications in prenat al diagnosis because of its reliability and speed. The identification of th e chromosomal origin of markers and unbalanced translocations provides the patient, physician, and genetic counselor with better predictive informatio n on the phenotype of the carrier.