Cytogenetic analysis: Is there a need to discover greater detail in the karyotype?

Chromosome studies are mandatory to confirm the diagnosis in even "typical" cases of genetic or malformation syndromes, since the phenotype does not unambiguously define the genotype. With the inception of banding methods to facilitate the unequivocal identification of chromosomes, major interest has been devoted to obtaining prometaphase chromosomes, since they allow for greater detail with a larger number of bands. The purpose of this study is to define in which circumstances prometaphase chromosome analysis is most useful and the minimum band level required for such high resolution detail in the karyotype. Karyotypes of 4 amniotic fluid samples and 14 prepheral blood specimens were prepared and studied at a range of band levels. The 18 cases were selected because of the presence of a variety of chromosomal anomalies. The results revealed that in most cases, a structural anomaly of a single chromosome could be surmised at banding level of 400-500. However, banding levels of 650-850 allowed for more clear delineation of the exact anomaly and accurate assignment of break points