Maternal uniparental isodisomy 11q13right-arrowqter in a dysmorphic and mentally retarded female with partial trisomy mosaicism 11q13right-arrowqter

EDITOR—Partial trisomy mosaicism describes the presence of a normal cell line together with an unbalanced translocation in a second cell line. Its incidence is not known. Only a few cases have been published,1 almost all with developmental delay and a pattern of dysmorphism. The presence of a normal cell line points towards postzygotic formation, but the origin and mechanism of formation have so far only been investigated in one case of partial trisomy 16p mosaicism and in another case of partial trisomy 21q mosaicism.2 3 In the former, a complex formation by trisomy first, translocation second, and uniparental disomy and partial trisomy third was inferred. In the latter, paternal meiotic origin of der(21;21)(q10;q10) mosaicism (46,XX/46,XX,der(21;21)(q10;q10),+21) in a girl with mild Down syndrome was described. Here, we report on a 25 year old woman with mental retardation, dysmorphic features, partial trisomy 11q13→qter mosaicism (46,XX, der(19)t(11;19)(q13;p13.3)/46,XX), maternal uniparental isodisomy 11q13→qter in the normal cell line, and two maternal and one paternal segment(s) 11q13→qter in the abnrmal cell line