Fluorescence in situ hybridization detection of two telomeres on the shortarm of a derived chromosome 16 in an infant with thrombocytopenia

We report a case of severe thrombocytopenia with an abnormal bone marrow ka ryotype described by G-banding analysis as t(16;21)(p?13;q11). Using fluore scence in situ hybridization (FISH) analysis with whole chromosome paints, the chromosome rearrangement was shown to be more complex, with the additio nal cryptic involvement of the long arm of chromosome 3. The chromosome rea rrangement involved the breakpoints 3q26, 16p13.3, and 21q11; this rearrang ement has not been previously described. The size of genomic material trans located from the chromosome 16 homologue was too small to be detected by ch romosome paint. A 16p-specific telomeric probe was hybridized to locate the translocated 16p material. The 16p telomeric unique sequence DNA was retai ned on the der(16) chromosome, indicating a more distal breakpoint. This st udy demonstrates that telomeric translocations con occur that would be unde tected by telomeric-specific FISH probes. (C) 2000 Elsevier Science Inc. Al l rights reserved.