FISH Diagnostics of Chromosomal Translocation with the Technology of Synthesis of Locus-Specific DNA Probes Based on Long-Range PCR

Detection of translocations in subtelomeric regions of chromosomes is a serious diagnostic problem, because they are difficult to determine by conventional cytogenetics with G banding. The aim of this work was the development of the technology of DNA probe synthesis for unique sequences of subtelomeric chromosome regions based on long-range PCR using the clinical case of determining the parental origin of unbalanced translocation between chromosomes 5 and 8. The unbalanced translocation der(5)t(5;8)(р15.33;q24.22) in a proband with physical, motor, intellectual, and speech development delay and in his sibling with speech and intellectual development delay as well, which was previously identified by array comparative genomic hybridization (aCGH), was confirmed by FISH. A balanced translocation 46,XX,t(5;8)(p15.33;q24.22) was detected in the mother’s karyotype using the created locus-specific DNA probe. This chromosome aberration was not detected by G banding of metaphase chromosomes. The father’s karyotype was normal according to FISH results. The method presented here makes it possible to create locus-specific DNA probes in a molecular cytogenetic laboratory using long-range PCR for the rapid diagnosis of cryptic chromosomal rearrangements.