Variable penetrance of the 15q11.2 BP1-BP2 microduplication in a family with cognitive and language impairment

The 15q11.2 BP1-BP2 region is found duplicated or deleted in people with cognitive, language, and behavioral impairment. Case presentation. We report on a family (the father and three male twin siblings) who presents with a duplication of the 15q11.2 BP1-BP2 region and a variable phenotype: whereas the father and the fraternal twin are normal carriers, the monozygotic twins exhibit severe language and cognitive delay and behavioral disturbances. The genes located within the duplicated region are involved in brain development and function, and some of them are related to language processing. Conclusions. The probands phenotype may result from changes in the expression level of some of these genes important for cognitive development.