Diagnostics Division, Center for DNA Fingerprinting and Diagnostics, Tuljaguda complex, 4-1-714, Hyderabad-500 001, Andhra-Pradesh, India.
Gene. 2012 Mar 10;495(2):199-204. doi: 10.1016/j.gene.2011.12.034. Epub 2011 Dec 28.
Down syndrome is a complex disorder characterized by well defined and distinctive phenotypic features. Approximately 2-3% of all live-born Down individuals are mosaics. Here we report a boy with suspected Down syndrome showing mosaicism for two different cell lines where one cell line is unexpected. The cytogenetic analysis by G-banding revealed a karyotype of 47 XY+21 [20]/46,X+marker [30]. Further, molecular cytogenetic analysis with spectral karyotyping identified the marker as a derivative of Y chromosome. The delineation of Y chromosomal DNA was done by quantitative real-time PCR and aneuploidy detection by quantitative fluorescence PCR. The Y-short tandem repeats typing was performed to estimate the variation in quantity as well as to find out the extent of deletion on Y chromosome using STR markers. Fluorescence in situ hybridization using Y centromeric probe was also performed to confirm the origin of the Y marker. Further fine mapping of the marker was carried out with three bacterial artificial chromosome clones RP11-20H21, RP11-375P13, RP11-71M14, which defined the hypothetical position of the deletion. In our study we defined the extent of deletion of the marker chromosome and also discussed it in relation with mosaicism. This is the first report of mosaic Down syndrome combined with a second de novo mosaic marker derived from the Y chromosome.
唐氏综合征是一种复杂的疾病,其特征是具有明确而独特的表型特征。大约 2-3%的所有唐氏综合征患者都是嵌合体。在这里,我们报告了一个疑似唐氏综合征的男孩,表现出两种不同细胞系的嵌合体,其中一种细胞系出乎意料。G 带核型分析显示核型为 47 XY+21 [20]/46,X+marker [30]。进一步的光谱核型分析表明,标记是 Y 染色体的衍生物。通过实时定量 PCR 进行 Y 染色体 DNA 的描绘,并通过定量荧光 PCR 进行非整倍体检测。进行 Y 短串联重复序列分型,以估计数量的变化以及使用 STR 标记确定 Y 染色体上的缺失程度。使用 Y 着丝粒探针进行荧光原位杂交也证实了 Y 标记的来源。使用三个细菌人工染色体克隆 RP11-20H21、RP11-375P13、RP11-71M14 对标记进行精细定位,确定了缺失的假设位置。在我们的研究中,我们确定了标记染色体的缺失程度,并讨论了其与嵌合体的关系。这是首例唐氏综合征嵌合体合并第二个源自 Y 染色体的新生嵌合标记的报告。