Recent Advances in Cytogenetic Technology for Antenatal Genetic Testing

The examination of human chromosomes has been a part of the physician’s laboratory armamentarium since the correct diploid number of human chromosomes was established and a method was developed for the in vitro growth of peripheral blood leukocytes to yield metaphase chromosomes. The discovery that on ultraviolet microscopy (UV), metaphase chromosomes stained with fluorochrome dyes displayed a characteristic pattern of bright and dull bands unique for a given pair of homologous chromosomes, was a major technological breakthrough in human cytogenetics; for the first time, every chromosome in the karyotype could be unequivocally identified. Although the short storage life of fluorochrome-stained chromosomes and the costs of UV microscopy have limited the usability of fluorescence banding, the introduction of one discriminating procedure quickly led to the development of an array of similar banding techniques for conventional microscopy that yield comparable information. Some of these technical procedures depend on enzyme and/or heat denaturation of the chromosomes, resulting in the characteristic banding patterns seen by the trypsin-Giemsa method, the 5M urea method, and the acid-saline-Giemsa technique. A typical human karyotype prepared from metaphase chromosomes treated with trypsin, stained with Giemsa, and photographed with brightfield photomicrographic techniques is shown in Figure 1. Careful examination of this karyotype reveals that each chromosome in the homologous pair has an array of dark and light bands identical with those of its homolog and that each homologous pair, autosomes number 1 to number 22, has a characteristic, easily identifiable banding pattern