A complex four-break rearrangement between chromosomes 4 and 13 resulting in a recombinant chromosome 4.

A complex four-break rearrangement between chromosomes 4 and 13 was ascertained in a 10-year-old mentally retarded girl. The rearrangement was inherited from the phenotypically normal mother, who had an inverted insertion of part of the long arm of chromosome 4 into the long arm of 13 and, in addition, a pericentric inversion of the deleted 4. Meiotic crossing-over between the normal and the inverted 4 resulted in a recombinant chromosome 4, which was inherited by the proband, together with the 13/4 insertion. In this way the proband became monosomic for 4q35 leads to qter and trisomic for 4pter leads to 4p15, but she showed only minor physical malformations, as compared with other reports on the trisomy 4p syndrome. The cytogenetic findings are difficult to describe using the ISCN nomenclature.