Multicolor banding remains an important adjunct to array CGH and conventional karyotyping

Array comparative genomic hybridization (CGH) for high resolution detection of chromosome imbalance, and karyotype analysis using G-banded chromosomes for detection of chromosome rearrangements, provide a powerful diagnostic armoury for clinical cytogenetics. However, abnormalities detected by karyotype analysis cannot always be characterised by scrutinising the G-banded pattern alone, and imbalance detected by array CGH cannot always be visualised in the context of metaphase chromosomes. In some cases further techniques are needed for detailed characterisation of chromosomal abnormalities. We investigated seven cases involving structural chromosome rearrangements detected by karyotype analysis, and one case where imbalance was primarily detected by array CGH. Multicolor banding (MCB) was used in all cases and proved invaluable in understanding the detailed structure of the abnormalities. Karyotype analysis detected structural chromosome rearrangements in 7 cases and MCB was used to help refine the karyotype for each case. Array CGH detected imbalance in an eighth case, where previously, G-banded chromosome analysis had reported a normal karyotype. Karyotype analysis of a second tissue type revealed this abnormality in mosaic form; however, MCB was needed in order to characterise this rearrangement. MCB provided information for the delineation of small deletions, duplications, insertions and inversions and helped to assign breakpoints which were difficult to identify from G-banded preparations due to ambiguous banding patterns. Despite the recent advance of array CGH in molecular cytogenetics we conclude that fluorescence in situ hybridization, including MCB, is still required for the elucidation of structural chromosome rearrangements, and remains an essential adjunct in modern diagnostic laboratories.