VIII.H.001

Chromosome microdissection plus micro-FISH analysis. Myelodysplasia. Step 1. G-banding to identify target abnormal chromosome. Karyotype contains ring chromosome of unknown origin. 46,XX, der11+ r. (See VIII.H.2 for Step 2.) der, derivative chromosome; r, ring chromosome.

VIII.H.002

Chromosome microdissection plus micro-FISH analysis. Step 2. This procedure is required to determine the origin of the ring chromosome, not identifiable on G banding. (A) Normal metaphase spread. The two arrows indicate the pair of chromosomes number 11. (B) Normal metaphase spread superimposed with micro-FISH probe hybridization. Chromosome microdissection is a method for identifying a chromosome segment of unknown origin. This process was initiated by dissection of the patient’s ring chromosome, accomplished by glass microneedles controlled by micromanipulators. After isolation, amplification by PCR, and fluorescence labeling, the probe was used to reverse chromosome paint the normal metaphase. The probe labeled the centromeric regions of both normal chromosomes number 11 from p13 to q13. (C) G-banding of patientâ s metaphase spread. Arrows point to ring chromosome and normal chromosome 11. (D) The micro-FISH probe was superimposed on the patient’s metaphase spread (forward chromosome painting) and the ring chromosome and the normal chromosome 11 from p13 to q13 (lower edge of figure) were painted. This result permitted assigning karyotype 46,XX,r(11)(p13q13). (E) Partial metaphase spread showing ring chromosome and normal chromosome 11 (arrows). (F) FISH probe hybridization superimposed on patient’s partial metaphase spread. The ring chromosome was larger than a single copy of the painted chromosome 11, so FISH was performed with a centromeric probe for chromosome 11. This step revealed the ring chromosome contained two centromeres of chromosome 11 (arrow). Thus, the karyotype was refined to 46,XX,der11,dic r11(:p13→q13::p13→q13:) Note also FISH centromeric probe identifying normal chromosome 11 (below the arrow). der, derivative chromosome; r, ring chromosome; dic, dicentric chromosome; FISH, fluorescence in situ hybridization.