Balkan Journal of Medical Genetics

TURNER SYNDROME WITH ISOCHROMOSOME Xq AND FAMILIAL RECIPROCAL TRANSLOCATION t(4;16)(p15.2;p13.1)
Cetin Z1, Mendilcioglu I2, Yakut S1, Berker-Karauzum S1,*, Karaman B3, Luleci G1
*Corresponding Author: Sibel Berker-Karauzum, Department of Medical Biology and Genetics, Faculty of Medicine, Akdeniz University, Antalya, Turkey; Tel.: +90-242-249-69-70; Fax: + 90-242-227-44-82/227-44-95; E-mail: sibelkarauzum@akdeniz.edu.tr
page: 57

DISCUSSION

The coexistence of a balanced translocation and a chromosome X abnormality in Turner syndrome patients is rarely reported in the literature [4-10]. Four cases were carriers of a parentally transmitted Robertsonian translocation and had the non mosaic 44,X,t(13;14)(q10;q10) karyotype [4-7]. Of these, three had inherited the translocation from their mothers and one from the father [4,7]. No other family members carried the translocation and sex chromosomal abnormality in these reports. There are three Turner syndrome patients with a familial balanced reciprocal translocation and monosomy of the X chromosome in the literature [8-10]. In these reports ,the reciprocal translocations were t(2;22)(q?;q?),t(1;22)(q32;q21) and t(8:19) (p21:p13), and no other family member was affected by sex chromosome abnormalities in two reports [9,10]. However, a boy with true hermaphroditism and 46,XX/46,XY mosaicism formed part of the family reported by Anneren et al. [8]. Our Turner syndrome patient had reciprocal translocation and structural abnormality of the X chromosome (isochromosome Xq). The clinical picture of our patient was mild and this finding is concordant with the previous reports indicating that most of the Turner syndrome patients with structural X chromosome abnormalities had mild phenotypes [12,13]. The numerical chromosome X abnormalities in low-level mosaic state observed in the mother was not associated with phenotypic abnormalities. However, the spontaneous abortion of the third pregnancy of the mother might be associated with the balanced translocation. As proposed by James et al. [14], the absence of a 46,XX cell line in our patient could suggest that a post-zygotic mechanism is not likely, unless the errors occurred during the first post-zygotic mitotic cell division. Alternatively, the patient may have been conceived with the karyotype 46,X,i(Xq) in a non mosaic state and a subsequent loss of the isochromosome from a proportion of cells resulted in the 45,X/46,X,i(Xq) karyotype [14]. There are several proposed mechanisms resulting in formation of isochromosome Xq. Generally, isochromosome Xq chromosomes are structurally dicentric chromosomes containing proximal Xp material suggesting that the most likely mechanism of formation is chromatid breakage and reunion in proximal Xp [15]. The more intense centromeric α satellite DNA signal on the isochromosome Xq observed in our case suggests that chromatid breakage and reunion in proximal Xp could be acceptable as a mechanism of formation in our case. Previous molecular genetic studies in patients with structural balanced translocations and monosomy X have excluded a meiotic non disjunction interchromosomal effect [4]. Unfortunately, we could not apply molecular genetic studies to show a possible effect of the maternal balanced translocation on the formation of isochromosome Xq because the family members were unavailable for further molecular genetic studies. As a result, in some Turner syndrome patients with structural chromosome X abnormalities accompanied by the familial transmitted balanced translocation, the carrier parents might have chromosome X abnormalities in a mosaic state. Therefore, the parental chromosomes should be evaluated to rule out possible low level numerical/structural chromosome X abnormalities which may be important for the management of further pregnancies.

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