Sachs E S, Jahoda M G, Los F J, Pijpers L, Wladimiroff J W
Department of Clinical Genetics, University Hospital Dijkzigt, Erasmus University, Rotterdam, The Netherlands.
Am J Med Genet Suppl. 1990;7:186-8. doi: 10.1002/ajmg.1320370737.
The recurrence risk for Down syndrome (DS) is about 1% in case of a previous offspring with trisomy 21 and minimal in case of a de novo (21;21) translocation. We have monitored 1,211 pregnancies in the first and second trimester after a prior occurrence of trisomy 21. Six couples had a trisomy 21 fetus in a subsequent pregnancy. We studied their lymphocytes, fibroblasts, and in one case ovaries, to detect parental mosaicism for chromosome 21. We detected mosaicism in 2 parents with 3 and 4 pregnancies, respectively, in which trisomy 21 was found. In one it was present in 47% of cells from the ovaries. Another couple with a pregnancy monitored because of a first child with a de novo (21;21) translocation had normal chromosomes themselves and one normal child, but 2 more pregnancies with a (21;21) translocation. It is concluded that thorough cytogenetic study of parents is indicated after 2 pregnancies with regular or translocation trisomy of chromosome 21. Genetic counseling should consider the possibility of an elevated recurrence risk due to gonadal mosaicism in one parent.
对于既往有21三体后代的情况，唐氏综合征（DS）的复发风险约为1%，而对于新发的（21;21）易位，复发风险则极低。我们对既往发生过21三体的1211例孕早期和孕中期妊娠进行了监测。六对夫妇在后续妊娠中有21三体胎儿。我们研究了他们的淋巴细胞、成纤维细胞，在一个案例中还研究了卵巢，以检测21号染色体的亲代嵌合体。我们在分别有3次和4次妊娠且发现21三体的2名父母中检测到了嵌合体。在其中一例中，卵巢细胞的47%存在嵌合体。另一对夫妇因第一个孩子为新发（21;21）易位而对妊娠进行监测，他们自身染色体正常且育有一个正常孩子，但另外2次妊娠均为（21;21）易位。结论是，在发生2次21号染色体常规三体或易位三体妊娠后，应对父母进行全面的细胞遗传学研究。遗传咨询应考虑到由于一方父母存在生殖腺嵌合体而导致复发风险升高的可能性。
