Molecular cytogenetic detection of trisomy 21 in interphase nuclei and metaphase chromosomes

Objective To explore the potential application of molecular methodology in the detection of numerical chromosome aberration for clinical diagnosis and prenatal diagnosis of Down's syndrome. Methods The primed in situ labelling (PRINS) procedure was carried out by i n situ annealing of specific oligonucleotide primers to chromosome 13, 16, 18, 21, X and Y, respectively, followed by primer elongation by a Tao polym erase in the presence of labelled nucleotides. Detection of the labelling s ites was performed by immunocytochemistry and conventional fluorescence mic roscopy. Results Under the stringent annealing temperature, chromosomes 13, 16, 18, X and Y were specifically labelled at centromeres and the procedure was car ried out successfully on interphase nuclei as well as on metaphase spreads with easily scorable signals. In 33 cases of uncultured peripheral blood ly mphocytes and 21 cases of uncultured amniocytes tested, two fluorescence si gnals were shown on more than 87.6% interphase nuclei when chromosomes 13, 16, 18 were investigated. Sex chromosomes were correctly detected in the sa me way. Blind tests on peripheral blood lymphocytes from 14 cases of normal individuals and 12 cases of Down's syndrome patients and on 9 Gases of amn iocytes showed that when chromosome 21 was detected by PRINS, two fluoresce nce spots as positive signals were visible on 89.3% normal nuclei and three spots on 88.8% trisomic nuclei. The above results were fully compatible wi th karyotypic analysis. Conclusion PRINS provides a rapid and efficient method for the clinical dia gnosis or prenatal diagnosis of trisomy 21.