DNA多态性诊断额外染色体和46,XX/46,XY嵌合体起源

Polymorphic detection of the origins of an extra chromosome and a 46,XX/46,XY chimerism

目的 :了解额外染色体和 4 6 ,XX/ 46 ,XY嵌合体的起源。 方法 :用短重复序列 (STR)分别对核型为 4 7,XX ,+2 1和 4 6 ,XX的一对孪生姐妹、4 7,XY ,+13男婴、4 6 ,XX/ 46 ,XY嵌合体的患儿进行检测。 结果 :4 7,XX ,+2 1和4 6 ,XX的孪生姐妹 15个STR位点检测显示有 8个位点不一致 ,孪生姐姐的D2 1S11位点有 3个微卫星标记物 ,其中2个源自母亲。 4 7,XY ,+13患儿的D13S317位点有 3个微卫星标记物 ,其中 2个源自父亲。 4 6 ,XX/ 46 ,XY患儿 8个位点显示父源的 2个微卫星标志物 ,13个位点显示母源的 1个标记物。 结论 :4 7,XX ,+2 1和 4 6 ,XX为双卵孪生姐妹 ,孪生姐姐额外 2 1号染色体源自母亲的第一次减数分裂不分离。 4 7,XY ,+13患儿额外 13号染色体源自父亲的第一次减数分裂不分离。 4 6 ,XX/ 46 ,XY患儿检测结果可解释为其母卵子经孤雌分裂产生了 2个DNA相同的配子 ,分别与X和Y精子受精 ,产生 2个合子在发育的早期阶段融合成 1个胚胎。

Objective:To investigate the origins of an extra chromosome and a 46,XX/46,XY chimerism. Methods:Short tandem repeats were detected from the twin girls with 47,XX,+21 and 46,XX, the neonatal boy with 47,XX,+13 and a chimerism with 46,XX/46,XY respectively. Results:The elder sister differed from younger sister in 8 STR loci. Three alleles were found from the elder sister in locus D21S11 and two from the mother. Three alleles were observed in the locus D13S317 from the neonatal boy with 47,XX,+13 and two from the father. With respect to the chimerism with 46,XX/46,XY, 8 STR loci clearly demonstrated the inheritance of the two paternal alleles and 13 STR loci of a single maternal allele in comparision with those of the parents. Conclusion:The twin girls originate from dizygote and the extra chromosome 21 of the elder sister is from nondisjunction during the first meiotic division of the mother. The extra chromosome 13 of the neonatal boy with 47,XX,+13 is from nondisjunction during the first meiotic division of the father .A parthenogenetic division of a haploid nucleus, to give two identical nuclei followed by fertilization of two spermatozoa and fusion of the two zyogate at early stage of life is the most likely explanation for the chimerism with 46,XX/46,XY.