P-14

Mosaicism with two X chromosome different rearrangements and a turner-like phenotype: case report

Sílvia Pires^I; Natália Oliva Teles^I,II; Manuela Mota Freitas^I,II; Cátia Cardoso^III; Maria da Luz Fonseca e Silva^I

^IUnidade de Citogenética, Centro de Genética Médica Doutor Jacinto Magalhães, Centro Hospitalar do Porto E.P.E., Porto, Portugal
^IIUnidade Multidisciplinar de Investigação Biomédica, ICBAS-UP
^IIIServiço de Pediatria, Hospital Central do Funchal, Funchal, Portugal

The frequency of Turner Syndrome (TS) has been reported as 1/5,000 live female births. This pathology  is most commonly associated with a 45,X karyotype but in approximately 25% of the patients the karyotype shows both a normal X and a structurally abnormal X chromosome. These abnormalities, which include deletions, duplications, inversions, translocations and ring chromosomes, imply chromosomal breaks and significant imbalance of gene content; they are generally benign because of the preferential inactivation of the abnormal X. Six to 15% of patients with TS are mosaics for an X ring chromosome [r(X)] line; however, in these cases the incidence of mental disability and other congenital abnormalities may be significantly higher. Some authors report that severe r(X) phenotypes can be seen in patients with active r(X) chromosomes lacking the X-inactive specific transcript  gene  (XIST  gene).The  authors  present a female patient aged 3 with clinical features of Turner syndrome. Cytogenetic studies revealed a novel mosaicism with two different abnormal cell lines: 1the major line with a normal X chromosome and another X with a rearrangement corresponding to a deletion of the distal region of the short arm (Xp) and duplication of the long arm (Xq13->qter); 2the other with a normal X chromosome and a r(X)(p22.3q13). FISH studies confirmed: in the line containing a rearranged X chromosome a deletion of the Xp subtelomeric region (Xp22.3) and a duplication of the Xq subtelomeric region (Xq28); in the line with r(X) a deletion of both subtelomeric regions. The presence of the XIST gene was demonstrated both in normal and abnormal X chromosomes, in the two cell lines.The authors will present a complete cytogenetic characterization of the patient and discuss all the factors that play an important role in determining the phenotypic outcome.