TWO PATIENTS WITH X CHROMOSOME DUPLICATION: dupXp AND dupXq
Ozer O1, Yilmaz Z1, Simsek E2, Derbent M3, Guner S3, Sahin FI1*
*Corresponding Author: Feride I. Sahin, Department of Medical Genetics, Faculty of Medicine, Baskent University, Kubilay sok. No: 36, 06570 Maltepe, Ankara, Turkey; Tel.: +90-312-232-44- 00/302; Fax: +90-312-231-91-34; E-mail: feridesahin@hotmail.com
page: 59

DISCUSSION

Abnormal X chromosomes that contain duplicated material can arise de novo or be of familial origin [2,6-8]. Most reported cases of X chromosome duplications that are phenotypically normal are familial, whereas those with abnormal phenotypes arise as de novo mutations [9]. This is consistentwith the findings in our patients. Patient 1 is regarded as familial with the duplicated X being inherited from the mother. In a familial case with dicentric inverted Xp duplication also inherited from the mother, the phenotype of the daughter was abnormal [10]. This is similar to our patient 1 who had phenotypic characteristics of the karyotype different from the mother. We suggest that submicroscopic rearrangements can be responsible for the phenotypic differences between the two generations. The similarity between mother and patient was menstrual irregularity. She was informed about the low possibility of becoming pregnant. If she should have a baby bowith an Xp duplication karyotype, he could be mentally retarded and may have an abnormal phenotype. Should she have a daughter with a similar karyotype, she may not necessarily be protected by selective X chromosome inactivation, and may therefore have phenotypic abnormalities. Most dup(Xq) females appear phenotypically normal, or may manifest with short stature, dysmorphic facial appearance and gonadal dysgenesis [11,12]. Patient 2 had growth retardation, feeding problems and vomiting but external genitalia were normal as reported in similar cases [9,11]. Recurrent infections in the respiratory or urinary tracts have been reported in male dup(Xq) cases [13-15]. A female patient with duplication from Xq12 to qter had otitis media during infancy [11]. Patient 2 had recurrent urinary tract infections. As the patient did not have any other bacterial or fungal infections such as pyodemia or supurative otitis, we concluded that recurrent urinary tract infections are coincidental and did not plan detailed immunologic test and quantitative immunoglobulin levels were not evaluated. The proximal region of Xq contains genes that normally escape X chromosome inactivation [6]. A two-fold increased expression of X-linked genes in Xq duplication patients has been reported [3,16,17]. Patient 2 with one breakpoint on Xq13, may have active genes in the duplicated region which lead to the phenotypic findings. Different inactivation patterns have also been reported in dup(X) patients [6,10,18]. In some cases there was full inactivation in all cells, in others a mosaic pattern of inactivation was observed [8,18,19]. Although selective X inactivation relatively diminishes phenotypic reflections, abnormal phenotypes could be observed in cases with pure dup(X) inactivation [9,19]. Epigenetic regulation of gene expression differs in the two arms of the X chromosome [19]. About 35% of genes on Xp were expressed, whereas only 5% were expressed on Xq [9,20]. The genes that escape inactivation have clinical significance as phenotype candidates in patients with X chromosome abnormalities [20]. While we observed a gonadal dysgenesis phenotype in our patient with the Xp duplication, our case with Xq duplication had a more severe phenotype which included mental retardation and multiple dysmorphic features. We think the clinical reflections will be illuminated, with more detailed studies of the genes located on the X chromosome.




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