A practical strategy for detection of major chromosome aneuploidies using ratio-mixing fluorescence in situ hybridization.

We describe the use of ratio-mixing FISH to visualize simultaneously probe sets specific for chromosomes 13, 18 and 21 as well as both sex chromosomes in uncultured lymphocytes and amniocytes. This method has the advantage of a smaller sample requirement than uni-colour FISH and potential for analysis of a larger number of chromosome aneuploidies using a minimum number of different probe haptenization and detection systems. An unselected series of uncultured lymphocytes and amniocytes was used to investigate the reliability of ratio-mixing FISH for diagnostic applications. The results indicate that the five-colour ratio-mixing FISH is a reliable technique and can be used for simultaneous detection of major aneuploidies. However, as a diagnostic approach, the strategy of using a three-colour ratio-mixing FISH and a dual colour to detect the five clinically important aneuploidies on two slides from the same sample, appears to be simpler and more practical.