Objective: To determine the efficacy of multicolor fluorescent in situ hybridization (M-FISH), which paints each chromosome in a unique color, for identification of congenital derivative and marker chromosomes. Material, Methods, and Cases: Commercially available M-FISH probes were used to label each chromosome in a specific fluorescent color. Six representative cases involving derivative chromosomes, markers, and subtle anomalies were analyzed by M-FISH. Results: Three familial, rather subtle derivative chromosomes were identified by M-FISH with relative ease. A small ring that was unidentifiable by bandedchromosome analysis was identified by M-FISH. A case of a subtle telomeric anomaly could not be resolved without the use of telomeric-specific probes. The M-FISH results were confirmed by individual chromosome-specific painting probes. Conclusion: M-FISH was helpful for identifying a wide range of congenital chromosomal anomalies. However, for subtle chromosomal abnormalities, use of locus-specific probes may be necessary.
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