COMPLEX CHROMOSOME REARRANGEMENT INVOLVING CHROMOSOME-1, CHROMOSOME-4AND CHROMOSOME-16 REVEALED BY FLUORESCENCE IN-SITU HYBRIDIZATION

A 7-year-old boy with mental retardation had apparently balanced recip rocal translocations, involving the telomeric regions of chromosomes 1 p and 49, which was detected by routine chromosome analysis. Fluoresce nce in situ hybridization (FISH) was used and also revealed the telome ric region of chromosome 16p to be involved in a still apparently bala nced translocation-complex, impossible to discover with classical cyto genetic analysis. We want to emphasize the importance of FISH in detec ting small chromosomal aberrations. We discuss whether the abnormal ph enotype is caused by unbalanced karyotype with cryptic undetected tran slocations or small deletions or mutations in the translocation-breakp oints.