Application of micro-FISH to delineate deletions

Microdissection combined with fluorescence in situ hybridization (micro-FISH) was used to visualize deletions in rearranged human chromosomes and in a de novo translocation. In each experiment five copies of a structurally aberrant chromosome or of the two chromosomes involved in the de novo translocation were isolated by microdissection and amplified using DOP-PCR. The PCR products were then used as probes for FISH to metaphase chromosomes of three patients. After reverse chromosome painting, the structurally aberrant chromosomes were completely painted, and the region deleted in the aberrant chromosomes was visible in the normal chromosomes. The smallest deletion that could be demonstrated this way was a microdeletion of ∼6 × 106 bp, which is frequently reported in Angelman and Prader-Willi syndromes.