Duplication of chromosome region 4q28.3-qter in monozygotic twins with discordant phenotypes

We describe monozygotic twins with partially discordant phenotypes who were found to have a duplication of chromosome region 4q28.3-qter. The duplicated region of chromosome 4 resulted from an unbalanced segregation of a balanced maternal (4;22)(q28.3;p13) translocation. Duplication of the long arm of chromosome 4 has been described in >60 patients; however, it usually results from the unbalanced segregation of a parental balanced translocation and has an associated monosomy. Twenty cases of dup 4q without an associated monosomy have been reported, and this is the only case of dup 4q28. 3-qter. All cases of dup 4q are reviewed, and phenotypic aspects are analyzed. Issues of monozygotic twinning and other birth defects also are addressed.