Wang J C, Nemana L, Kou S Y, Habibian R, Hajianpour M J
Alfigen/The Genetics Institute, Pasadena, California 91105, USA.
Am J Med Genet. 1997 Sep 5;71(4):463-6.
Monosomy of the entire short arm of chromosome 18 as a result of an 18;acrocentric whole arm translocation has been reported in over 20 patients, 3 of which were familial. The centromeric origin in de novo cases has not been characterized. We report molecular cytogenetic studies of two prenatally-detected de novo cases. Amniocenteses were performed because of sonographic findings of fetal holoprosencephaly. Cytogenetic studies and dual color fluorescence in situ hybridization using Oncor alpha-satellite probes for D18Z1 and D13Z1/D21Z1 showed monosomy 18p with presence of a dicentric 18;21 chromosome in both cases [45,XY,dic(18;21)(p11.1;p11.1)]. In one case, a second cell line was found, which contained 46 chromosomes with a del(18)(p11.1) and an apparently telocentric 21 not present in either parent [46,XY,del(18)(p11.1),del(21)(p11.1)]. The del(18)(p11.1) contained only the 18 alphoid sequence and the telocentric 21 contained only the 21 alphoid sequence. No centromeric break was detected. We propose that the second cell line arose from dissociation of the dic(18;21) with no centromeric DNA break. In addition to our case, there have been three previous reports of dissociation of dicentric 18;acrocentric chromosomes indicating that the translocation site can be unstable and dissociate.
据报道，因18号染色体与近端着丝粒染色体发生全臂易位导致18号染色体短臂单体型的患者已超过20例，其中3例为家族性病例。新发病例的着丝粒起源尚未明确。我们报告了两例产前检测到的新发病例的分子细胞遗传学研究。因超声检查发现胎儿前脑无裂畸形而进行了羊膜穿刺术。细胞遗传学研究以及使用针对D18Z1和D13Z1/D21Z1的Oncorα卫星探针进行的双色荧光原位杂交显示，两例均为18p单体型，伴有一条双着丝粒18;21染色体[45,XY,dic(18;21)(p11.1;p11.1)]。在其中一例中，发现了第二个细胞系，其含有46条染色体，带有del(18)(p11.1)和一条父母双方均未出现的明显端着丝粒21号染色体[46,XY,del(18)(p11.1),del(21)(p11.1)]。del(18)(p11.1)仅包含18号染色体的α卫星序列，端着丝粒21号染色体仅包含21号染色体的α卫星序列。未检测到着丝粒断裂。我们推测第二个细胞系源自双着丝粒18;21染色体的解离，且未发生着丝粒DNA断裂。除我们的病例外，此前还有3篇关于双着丝粒18号染色体与近端着丝粒染色体解离的报道，表明易位位点可能不稳定并发生解离。
