Characterization of an unbalanced de novo rearrangement by microsatellite polymorphism typing and by fluorescent in situ hybridization.

Unbalanced de novo rearrangements, difficult to characterize by conventional cytogenetic techniques, may be elucidated by molecular approaches. By dinucleotide repeat polymorphism typing and fluorescence in situ hybridization (FISH), we have defined the composition of an unbalanced de novo translocation (46,XX,15p+) in a child with multiple congenital anomalies. Use of a microsatellite repeat D5S208 (localized to 5p15) and polymerase chain reaction (PCR) analysis confirmed that the extra segment originated from the short arm of chromosome 5. Amplification of the patient's DNA with primers for dinucleotide repeats D5S350 and D5S118 showed that the entire 5p (from 5pter to 5q11) was present in 3 copies. FISH confirmed the trisomic status of 5p, and further revealed the presence of centromeres of both chromosomes 5 and 15 on the rearranged chromosome thus delineating its dicentric nature. This information allowed us to redefine the de novo rearrangement in this patient as 46,XX,dic der(15)t(5;15)(q11;p11).