Micale M A, Wolff D J, Dickerman L H, Redline R, Conroy J M, Schwartz S
Department of Genetics, Case Western Reserve University School of Medicine, Cleveland, OH, USA.
Prenat Diagn. 1996 Oct;16(10):893-7. doi: 10.1002/(SICI)1097-0223(199610)16:10<893::AID-PD962>3.0.CO;2-M.
We report a case of mosaic trisomy 20, the most common autosomal mosaicism identified in amniocytes, ascertained in a woman referred for amniocentesis because of abnormal ultrasound at 18.1 weeks' gestation which revealed short femurs and nuchal thickening. Metaphase analysis of 98 clones revealed 47,XY, +20 in 96 cells (98 per cent). Trisomy 20 was demonstrated in 6 cells (12 per cent) in a total of 50 cells from two fetal blood cultures obtained after pregnancy termination. Fluorescence in situ hybridization (FISH) analysis of interphase nuclei utilizing a chromosome 20 alpha-satellite centromeric DNA probe revealed three signals in 57/546 nuclei (10 per cent) in fetal blood. Metaphase analysis of 167 cells from seven different fetal tissue sources revealed trisomy 20 in 32 cells (19.2 per cent). The percentage of trisomy 20 cells varied with tissue type, with the highest percentage (13/25 cells, 52 per cent) identified in the small intestine and lymph nodes and the lowest percentage (1/34 cells, 2.9 per cent) identified in a specimen of chorionic villi. Molecular genetic analyses utilizing polymerase chain reaction (PCR)-formated dinucleotide repeat polymorphisms demonstrated that the non-disjunctional event most likely occurred post-zygotically and that the origin of the extra chromosome 20 was maternal. This study is the first to demonstrate trisomy 20 cells in fetal blood, suggesting that mosaic trisomy 20 can be embryonic in origin. In cases of prenatally detected mosaic trisomy 20, examination of fetal blood should be considered, as well as study of placental membranes, skin, and urine sediment to confirm the karyotype and determine its significance.
我们报告一例20号染色体三体嵌合体病例，这是羊水中最常见的常染色体嵌合体。该病例是一名妊娠18.1周的女性，因超声检查异常转诊接受羊膜穿刺术，超声显示股骨短小和颈部增厚。对98个克隆进行中期分析，发现96个细胞（98%）为47,XY, +20。终止妊娠后从两份胎儿血培养物中获取的总共50个细胞中，有6个细胞（12%）显示20号染色体三体。利用20号染色体α卫星着丝粒DNA探针进行间期核荧光原位杂交（FISH）分析，发现胎儿血中57/546个核（10%）有三个信号。对来自七个不同胎儿组织来源的167个细胞进行中期分析，发现32个细胞（19.2%）有20号染色体三体。20号染色体三体细胞的百分比因组织类型而异，在小肠和淋巴结中比例最高（13/25个细胞，52%），在绒毛膜绒毛标本中比例最低（1/34个细胞，2.9%）。利用聚合酶链反应（PCR）格式的二核苷酸重复多态性进行分子遗传学分析表明，不分离事件很可能发生在合子后，额外的20号染色体来源于母亲。本研究首次在胎儿血中证实20号染色体三体细胞，提示20号染色体三体嵌合体可能起源于胚胎。对于产前检测到的20号染色体三体嵌合体病例，应考虑检查胎儿血，以及研究胎盘膜、皮肤和尿沉渣，以确认核型并确定其意义。
