Laboratory for Cytogenetics, Center for Genetic Counseling, Buddhist Tzu Chi General Hospital, Hualien, Taiwan.
BMC Med Genet. 2012 Sep 20;13:85. doi: 10.1186/1471-2350-13-85.
Approximately 30 sex-chromosome discordant chimera cases have been reported to date, of which only four cases carried trisomy 21. Here, we present an additional case, an aborted fetus with a karyotype of 47,XX, +21/46,XY.
Autopsy demonstrated that this fetus was normally developed and had male genitalia. Major characteristics of Down syndrome were not observed except an enlarged gap between the first and second toes. Karyotyping of tissues cultured from the fetus revealed the same chimeric chromosomal composition detected in the amniotic fluid but with a different ratio of [47,XX,+21] to [46,XY]. Further short tandem repeat analysis indicated a double paternal contribution and single maternal contribution to the fetus, with the additional chromosome 21 in the [47,XX,+21] cell lineage originating from the paternal side.
We thus propose that this chimeric fetus was formed via the dispermic fertilization of a parthenogenetic ovum with one (Y) sperm and one (X,+21) sperm.
迄今为止，已经报道了大约 30 例性染色体不同的嵌合体病例，其中只有 4 例携带三体 21。在此，我们报告另外一例嵌合体病例，为一流产胎儿，其核型为 47,XX,+21/46,XY。
尸检显示该胎儿发育正常，具有男性外生殖器。除了第一和第二脚趾之间的间隙增大外，未观察到唐氏综合征的主要特征。对胎儿组织培养进行的核型分析显示，与羊水检测到的嵌合染色体组成相同，但[47,XX,+21]与[46,XY]的比例不同。进一步的短串联重复分析表明，胎儿存在双亲双源单母的遗传特征，额外的 21 号染色体来自父源。
因此，我们提出这个嵌合体胎儿是由一个（Y）精子和一个（X,+21）精子孤雌激活的部分二倍体卵子受精形成的。
