RT Journal Article SR Electronic T1 Molecular and cytogenetic characterisation of an unusual case of partial trisomy/partial monosomy 13 mosaicism: 46,XX,r(13)(p11q14)/46,XX,der(13)t(13;13)(q10;q14) JF Journal of Medical Genetics JO J Med Genet FD BMJ Publishing Group Ltd SP 77 OP 82 DO 10.1136/jmg.36.1.77 VO 36 IS 1 A1 Mattia Gentile A1 Antonia L Buonadonna A1 Filomena Cariola A1 Paola Fiorente A1 Maria C Valenzano A1 Ginevra Guanti YR 1999 UL http://jmg.bmj.com/content/36/1/77.abstract AB A female infant with multiple malformations and mental retardation was noted to have a rare de novo chromosome abnormality involving mosaicism with two cell lines, one with a ring chromosome 13, and the other with partial trisomy 13 owing to a complex rearrangement. Cytogenetic examination excluded the presence of a t(13q;13q) cell line and showed a cell line with a marker chromosome containing two chromosome 13 long arms joined together after deletion of a part (q11→q14) of one of them. In addition, the absence of a cell line with two normal chromosomes 13 or a cell line with a t(13q;13q) implies that the ring (13) and the marker (13) arose from a single event at the first cleavage division. The two cell lines were present in different proportions in both peripheral blood lymphocytes and skin fibroblasts. The results of microsatellite characterisation clearly indicate the paternal origin and the absence of recombination, supporting the postzygotic origin of both the ring and the marker chromosome.