THE ORIGIN OF CYTOLOGICALLY UNIDENTIFIABLE CHROMOSOME-ABNORMALITIES -6 CASES ASCERTAINED BY TARGETED CHROMOSOME-BAND PAINTING

De novo chromosome structural abnormalities cannot always be diagnosed by the use of standard cytogenetic techniques. We applied a previousl y developed chromosome-band-specific painting method to the diagnosis of such rearrangements. The diagnostic procedures consisted of microdi ssection of an aberrant chromosomal region of a given patient, polymer ase chain reaction (PCR) amplification of the dissected chromosomal DN A, and subsequent competitive fluorescence in situ hybridization (FISH ) using the PCR products as a probe pool on metaphase chromosomes from the patient and/or a karyotypically normal person. With this strategy , we studied 6 de novo rearrangements (6p+, 6q+, 9p+, 17p+, +mar, and +mar) in 6 patients. These rearrangements had been seen by conventiona l banding but their origin could not be identified. In all 6 patients, we successfully ascertained the origin. Using an aberrant region-spec ific probe pool, FISH signals appeared on both the aberrant region and a region of another specific chromosome pair. A reverse probe pool th at was generated through the microdissection of normal chromosomes at a candidate region for the origin of the aberration hybridized with bo th the aberrant and the candidate regions. We thus diagnosed one patie nt with 17p+ as having trisomy for 14q32-qter, one with 9p+ as having trisomy for 12pter-p12, one with 6q+ as having a tandem duplication (t risomy) of a 6q23-q25 segment, one with 6p+ as having a tandem duplica tion (trisomy) of a 6p23-q21.3 segment, one with a supernumerary metac entric marker chromosome as having tetrasomy for 18pter-cen, and the l ast with an additional small marker chromosome as having trisomy for 1 8p11.1 (or p11.2)-q11.2. The present targeted chromosome-band-painting method provides the simple and rapid preparation of a probe pool for region-specific FISH, and is useful for the diagnosis of chromosome ab normalities of unknown origin.