Genuardi M, Tozzi C, Pomponi M G, Stagni M L, Della Monica M, Scarano G, Calvieri F, Torrisi L, Neri G
Istituto di Genetica Medica, Facoltà di Medicina e Chirurgia A Gemelli, Università Cattolica del S Cuore.
Eur J Hum Genet. 1999 May-Jun;7(4):421-6. doi: 10.1038/sj.ejhg.5200333.
Mosaicism for trisomy 17 in amniocyte cultures is a rare finding, whilst postnatal cases are exceptional. In order to gain insight into the possible effects of the distribution of the trisomic line and of uniparental disomy (UPD) on embryofoetal development, we have performed follow-up clinical, cytogenetic and molecular investigations into three newly detected prenatal cases of trisomy 17 mosaicism identified in cultured amniotic fluid. In the first case, the pregnancy ended normally with the birth of a healthy girl, and analysis of newborn lymphocytes and of multiple extra-embryonic tissues was indicative of confined placental mosaicism. The second case was also associated with a normal pregnancy outcome and postnatal development, and only euploid cells were found in peripheral blood after birth. However, maternal isodisomy 17 consequent to a meiosis II error and loss of a chromosome 17 homologue was detected in peripheral lymphocytes postnatally. In the third case, pathological examination after termination of pregnancy showed growth retardation and minor dysmorphisms, and the trisomic line was detected in foetal skin fibroblasts. In addition, biparental derivation of chromosome 17 was demonstrated in the euploid lineage. These results, together with previously reported data, indicate that true amniotic trisomy 17 mosaicism is more commonly of extra-embryonic origin and associated with normal foetal development. Phenotypic consequences may arise when the trisomic line is present in foetal tissues. Case 2 also represents the first observation of maternal UPD involving chromosome 17; the absence of phenotypic anomalies in the child suggests that chromosome 17 is not likely to be subject to imprinting in maternal gametes.
羊膜细胞培养中17三体嵌合体是一种罕见发现，而出生后病例则更为罕见。为了深入了解三体细胞系分布和单亲二体（UPD）对胚胎胎儿发育的可能影响，我们对在培养羊水样本中新检测出的三例17三体嵌合体产前病例进行了临床、细胞遗传学和分子学随访研究。第一例中，妊娠正常结束，娩出一名健康女婴，对新生儿淋巴细胞和多个胚外组织的分析表明为局限性胎盘嵌合体。第二例也有正常的妊娠结局和产后发育，出生后外周血中仅发现整倍体细胞。然而，出生后在外周淋巴细胞中检测到因减数分裂II错误导致的母源17号染色体等二体及一条17号染色体同源染色体的丢失。第三例中，妊娠终止后的病理检查显示生长发育迟缓及轻微畸形，在胎儿皮肤成纤维细胞中检测到三体细胞系。此外，在整倍体谱系中证实了17号染色体的双亲来源。这些结果与先前报道的数据一起表明，真正的羊膜17三体嵌合体更常见于胚外起源并与正常胎儿发育相关。当三体细胞系存在于胎儿组织中时可能会出现表型后果。病例2也是母源17号染色体单亲二体的首次观察；该儿童无表型异常表明17号染色体在母源配子中不太可能受到印记影响。
