Bartels I, Schlueter G, Liehr T, von Eggeling F, Starke H, Glaubitz R, Burfeind P
Institute of Human Genetics, University of Göttingen, Göttingen, Germany.
Cytogenet Genome Res. 2003;101(2):103-5. doi: 10.1159/000074163.
Trisomy rescue is one of various proposed mechanisms in formation of supernumerary small marker chromosomes (SMC) and uniparental disomy (UPD). In the present report a small de novo marker chromosome derived from chromosome 14 or 22 was diagnosed at prenatal diagnosis due to maternal age. Follow up investigations at birth revealed mosaicism 47,XX,+mar/46,XX. Using FISH, the marker was positive for the probe D14/22Z1, but negative for the probes midi 54 and D22Z4. Using three informative markers both chromosomes 22 were shown to be inherited from the mother (UPDmat). The results are consistent with nondisjunction at maternal meiosis I. The girl is 18 months old now and phenotypically normal. Cardiac and abdominal malformations were excluded by sonographic examinations. Motor and mental development is according to or ahead of developmental milestones (free walking with 10 months, first words at 12 months). The case confirms that maternal UPD 22 most likely is not associated with clinical abnormalities. According to FISH results, UPD 22, and 47,XX,+22 in the placenta, we conclude that the SMC was derived from alpha satellite sequences of chromosome 22. This case for the first time gives evidence that early postzygotic reduction of a chromosome to a small marker chromosome is a real existing mechanism to rescue a conceptus with trisomy.
三体挽救是在额外小标记染色体（SMC）和单亲二体（UPD）形成过程中提出的多种机制之一。在本报告中，由于孕妇年龄，在产前诊断时诊断出一条源自14号或22号染色体的新生小标记染色体。出生后的随访调查显示为嵌合体47,XX,+mar/46,XX。使用荧光原位杂交（FISH）技术，该标记对探针D14/22Z1呈阳性，但对探针midi 54和D22Z4呈阴性。使用三个信息性标记物显示两条22号染色体均从母亲遗传而来（母源UPD）。结果与母源减数分裂I期的不分离一致。该女孩现在18个月大，表型正常。超声检查排除了心脏和腹部畸形。运动和智力发育符合或超前于发育里程碑（10个月会独立行走，12个月会说第一个单词）。该病例证实母源UPD 22最有可能与临床异常无关。根据FISH结果、胎盘内的UPD 22和47,XX,+22，我们得出结论，该SMC源自22号染色体的α卫星序列。该病例首次证明合子后早期将一条染色体减少为小标记染色体是挽救三体胚胎的一种实际存在的机制。
