Molecular cytogenetic characterization of an insertional translocation, ins(6;7)(p25;q33q34): deletion/duplication of 7q33-34 and clinical correlations.

A balanced insertional translocation between chromosomes 6 and 7, ins(6;7)(p25;q33q34) has been extensively investigated. The insertional translocation was found in several members of a three-generation family, where some were healthy balanced carriers while others had clinical symptoms due to deletion or duplication of 7q33-34. The deleted/duplicated segment could only be detected using high resolution banding and fluorescent in situ hybridization. A number of BAC/PAC clones located on chromosome 6 and 7 were used to characterize the breakpoint regions in detail and to determine the size of the deletion, which was 7.6 Mb, containing up to 68 genes. However, the insert on chromosome 6 was only 7.4 Mb, due to a deletion of 227 kb at the distal breakpoint on 7q. This small deletion was also found in the "balanced" carriers, and although the chromosome segment contains at least eight genes, none of the carriers seem to be affected by haploinsufficiency, since the phenotype is apparently normal. This is the first detailed characterization and phenotype correlation of such a deletion/duplication of distal 7q.