(Figs. 2 and 3) CYTOGENETIC INTERPRETATION
Chromosome analysis and fish studies performed revealed the following:
Classical cytogenetic showed an unbalanced karyotype, of a female, with forty-six chromosomes and an additional chromatin segment attached to the short (p) arm of 18. FISH studies were then performed using a class of DNA probes known as "paint" probes in order to further delineate the derivative 18 chromosome. Each paint probe contains multiple DNA sequences corresponding to a specific chromosome. This class of probe is particularly useful in identifying unknown regions of DNA, such as cryptic translocations, duplications, insertions, or marker chromosomes. The paint probes for multiple chromosomes including chromosomes 5, 7, 10, 18, and 21 were used for FISH analysis on this patient. FISH with the chromosome 18 whole chromosome paint (wcp18) (Figs. 4 and 5) showed hybridization to the entire normal chromosome 18 and only to the long arm (q) and a small part of the short (p) arm of the derivative #18. The part of the derivative chromosome 18 that did not hybridize to the wcp (18) probe showed hybridization with the paint probe for chromosome 5 (Fig. 6).
Subsequently, telomere-specific probes for the chromosome 5 p telomere and 5q telomere were used in order to determine if the chromosome 5 material on the derivative 18 originated from the short arm or the long arm of chromosome 5. Hybridization was positive for the chromosome 5 p telomere probe indicating that the extra material was derived from the short arm of chromosome 5. (Fig. 7) Fish with short arm and long arm of 5 telomere probes (Fig. 8) determined that the short arm region of chromosome 5 was involved in the translocation with chromosome 18.