REPLICATION BANDING AND MOLECULAR STUDIES OF A MOSAIC, UNBALANCED DIC(X-15)(XPTER-]XQ26.1 /15P11-]15QTER)/

We present a patient with a chromosomal mosaicism involving the X chro mosome, One cell line is 45,X and the other has a de novo paternally d erived dicentric X;15 translocation, Her karyotype is therefore 45,X/4 5,X,dic(X;15)(Xpter-->Xq26.1::15p11-->15 qter) based on G-banding. The presence of 2 centromeres on the derivative X was confirmed by fluore scence in situ hybridization (FISH) and a deletion of Xq26.1-->qter wa s confirmed by polymerase chain reaction (PCR) using DXS52 and DXYS154 . Replication banding studies indicate that the derivative X is late r eplicating, Based on these studies, it is unclear whether inactivation has spread to proximal 15q. The patient has a unique phenotype distin ct from Ullrich-Turner or Prader-Willi syndromes, but includes ataxia and language delay which are commonly seen in Angelman syndrome, These findings are contrary to those anticipated since deficiency of patern al genes at 15q12 typically leads to Prader-Willi syndrome, Molecular analysis of PCR-based polymorphisms of chromosome 15 and X indicates t hat uniparental disomy is not present for the X chromosome or chromoso me 15 in either cell line, It is hypothesized that her phenotype resul ts from the interaction of the 2 abnormal genotypes, Each abnormality may be diluted by the mosaicism and, in the derivative X line, by the possible variation among cells of inactivation spreading to chromosome 15. (C) 1995 Wiley-Liss, Inc.