A t(7;12) balanced translocation with breakpoints overlapping those of the Williams-Beuren and 12q14 microdeletion syndromes

The molecular characterization of balanced chromosomal rearrangements have always been of advantage in identifying diseasecausing genes. Here, we describe the breakpoint mapping of a de novo balanced translocation t(7;12)(q11.22;q14.2) in a patient presenting with a failure to thrive associated with moderate mental retardation, facial anomalies, and chronic constipation. The localization of the breakpoints and the co-occurrence of Williams - Beuren syndrome and 12q14 microdeletion syndrome phenotypes suggested that the expression of some of the dosagesensitive genes of these two segmental aneuploidies were modified in cells of the proposita.However, we were unable to identify chromosomes 7 and/or 12-mapping genes that showed disturbed expression in the lymphoblastoids of the proposita. This case showed that position-effect might operate in some tissues, but not in others. It also illustrates the overlap of phenotypes presented by patients with the recently described 12q14 structural rearrangements.