A 15 leads to 1 translocation in a patient mosaic for presence or absence of an isodic(15p)(q11).

We report a patient with a 15 leads to 1 translocation who was mosaic for presence or absence of an isodic(15p)(q11). Her phenotype is similar to that of patients with deletions of proximal 15q or isodic(15p). Several phenotypes, including the Prader-Labhart-Willi syndrome, have been described with abnormalities of proximal 15q and have in common severe hypotonia, developmental delay, and lack of major congenital anomalies. Our patient is the first to be described with an isodic (15p)(q11) associated with a nonreciprocal translocation. We think her isodic(15p)(q11) arose as a result of a sister chromatid fusion rather than nonsister chromatid exchange as has been proposed in most other cases. Because of the various phenotypes described with proximal 15q abnormalities, we recommend caution in the assignment of specific phenotypes to small chromosome changes in this area.