P15

Distal XQ27->Q28 duplication and functional disomy: clinical and cytogenetic characterization

Fernanda Paula Oliveira^I; Maria do Céu Ribeiro^I; Natália Oliva Teles^I,II; Ana Maria Fortuna^III; Maximina Rodrigues Pinto^I; 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
^IIIUnidade de Genética Médica, Centro de Genética Médica Doutor Jacinto Magalhães, Centro Hospitalar do Porto E.P.E., Porto, Portugal

Distal Xq duplications are intrachromosomal disorders that constitute the main cause of functional disomy in males. Most cases are inherited from heterozygote mothers. These duplications vary in size, location and gene content of the correspondent segment. Hemizygous male descendents have a functional partial Xq disomy and are phenotipically abnormal. A male proband aged  7  months  was  referred for cytogenetic studies due to psychomotor delay, coarse features and cardiopathy. Both the child and the mother’s karyotypes were obtained from peripheral blood lymphocyte cultures using standard techniques  and  chromosomes were analysed with GTG banding. The child’s mother was studied using fluorescence in situ hybridization (FISH) with a whole chromosome painting probe for the X chromosome (wcpX, Cytocell), to exclude the involvement of any other chromosome and X inactivation pattern techniques. Karyotypes were requested for the mother’s parents. The cytogenetic analysis revealed extra material on the long arm of the X chromosome both in the proband and in the mother. Maternal grandparents had normal karyotypes. X inactivation studies in the mother showed that the abnormal X was always late replicating and therefore inactive. No further testing was possible in the child, since he deceased of pneumonia at the age of 8 months. The extra material observed in the distal segment of the long arm of the X chromosome in this family was interpreted as a duplication of chromosome X terminal region (q27.3->q28). Child’s final karyotype: 46,Y,dup(X) (q27.3-q28)mat.Large cytogenetic visible duplications of Xq are rare, the most common being the Xq27->q28 region and there are only about 40 cases described in the literature. The prevalence of Xq duplications  is  still  unknown  but the clinical outcome is a well recognized phenotype. The proness to infections in  individuals with this condition is almost invariably the cause of death in childhood. The clinical history and cytogenetic findings of this case are in agreement with similar cases previously reported. Parents were given appropriate genetic counselling and offered the possibility of prenatal genetic diagnosis in future pregnancies. Since then, two healthy 46,XX daughters were born.