Petković Iskra, Barisić Ingeborg, Bastić Mislav, Hećimović Silva, Bago Ruzica
University Children's Hospital Zagreb, Zagreb, Croatia.
Am J Med Genet A. 2003 Jul 15;120A(2):266-71. doi: 10.1002/ajmg.a.20017.
We present a case of trisomy for the whole short arm of chromosome 6 in a 3-year-old girl with moderate mental retardation, mild facial dysmorphism, short stature, failure to thrive, and no abnormalities of the visceral organs. Cytogenetic and fluorescence in situ hybridization (FISH) analysis revealed a 46, X, der(X)t(X;6)(q22; p11.1) karyotype. The derived X was late replicating with variable spreading of X chromosome inactivation onto the translocated 6p. A normal karyotype was observed in the father, while the mother presented 46,XX/46,XX, der(10)t(6;10)(p11;p11). The mother is a mosaic with unbalanced t(6;10) in 4.7% of cells. To the best of our knowledge, this unusual mosaicism has not yet been reported. In this family the short arm of chromosome 6 was involved in an unbalanced rearrangement with chromosome X in the proband and with chromosome 10 in the mother. In order to study the mechanism of the formation of t(X;6) in the girl we performed DNA polymorphism analysis. These investigations revealed that chromosomes X and 6 involved in the rearrangement are of paternal origin. Our patient exhibits only discrete facial features characteristic of partial trisomy 6p. We suggest that mild phenotypic expression be probably due to X chromosome inactivation spreading onto the translocated 6p. This report show that combined cytogenetic, FISH, and molecular analysis of chromosomal aberrations are necessary for the understanding of the mechanism of formation, parental origin, and genetic counseling.
我们报告了一例3岁女童6号染色体短臂三体的病例，该女童有中度智力发育迟缓、轻度面部畸形、身材矮小、生长发育不良，内脏器官无异常。细胞遗传学和荧光原位杂交（FISH）分析显示核型为46,X,der(X)t(X;6)(q22;p11.1)。衍生的X染色体复制延迟，X染色体失活可变地扩展到易位的6p上。父亲核型正常，而母亲的核型为46,XX/46,XX,der(10)t(6;10)(p11;p11)。母亲是嵌合体，4.7%的细胞中有不平衡的t(6;10)。据我们所知，这种不寻常的嵌合体尚未见报道。在这个家族中，6号染色体短臂在先证者中与X染色体发生不平衡重排，在母亲中与10号染色体发生不平衡重排。为了研究该女孩中t(X;6)的形成机制，我们进行了DNA多态性分析。这些研究表明，参与重排的X染色体和6号染色体均来自父亲。我们的患者仅表现出部分6p三体特征性的离散面部特征。我们认为轻度表型表达可能是由于X染色体失活扩展到易位的6p上。本报告表明，联合细胞遗传学、FISH和染色体畸变的分子分析对于理解形成机制、亲本来源和遗传咨询是必要的。
