Vorsanova Svetlana G, Iourov Ivan Y, Voinova-Ulas Victoria Y, Weise Anja, Monakhov Victor V, Kolotii Alexei D, Soloviev Ilia V, Novikov Petr V, Yurov Yuri B, Liehr Thomas
Institute of Human Genetics and Anthropology, Friedrich Schiller University, Jena, Germany.
Mol Cytogenet. 2008 Jun 19;1:13. doi: 10.1186/1755-8166-1-13.
Autosomal monosomies in human are generally suggested to be incompatible with life; however, there is quite a number of cytogenetic reports describing full monosomy of one chromosome 21 in live born children. Here, we report a cytogenetically similar case associated with congenital malformation including mental retardation, motor development delay, craniofacial dysmorphism and skeletal abnormalities.
Initially, a full monosomy of chromosome 21 was suspected as only 45 chromosomes were present. However, molecular cytogenetics revealed a de novo unbalanced translocation with a der(7)t(7;21). It turned out that the translocated part of chromosome 21 produced GTG-banding patterns similar to original ones of chromosome 7. The final karyotype was described as 45,XX,der(7)t(7;21)(q34;q22.13),-21. As a meta analysis revealed that clusters of the olfactory receptor gene family (ORF) are located in these breakpoint regions, an involvement of OFR in the rearrangement formation is discussed here.
The described clinical phenotype is comparable to previously described cases with ring chromosome 21, and a number of cases with del(7)(q34). Thus, at least a certain percentage, if not all full monosomy of chromosome 21 in live-borns are cases of unbalanced translocations involving chromosome 21.
一般认为人类常染色体单体性与生命不相容；然而，有相当多的细胞遗传学报告描述了活产儿中一条21号染色体的完全单体性。在此，我们报告一例细胞遗传学上类似的病例，伴有先天性畸形，包括智力发育迟缓、运动发育延迟、颅面畸形和骨骼异常。
最初，由于仅存在45条染色体，怀疑为21号染色体完全单体性。然而，分子细胞遗传学显示存在一个新生的不平衡易位，形成der(7)t(7;21)。结果发现，21号染色体的易位部分产生的GTG带型与7号染色体的原始带型相似。最终核型描述为45,XX,der(7)t(7;21)(q34;q22.13),-21。由于荟萃分析显示嗅觉受体基因家族（ORF）的簇位于这些断裂点区域，本文讨论了OFR参与重排形成的情况。
所描述的临床表型与先前报道的21号环状染色体病例以及一些7号染色体长臂缺失（del(7)(q34)）病例相似。因此，活产儿中至少有一定比例（如果不是全部）的21号染色体完全单体性病例是涉及21号染色体的不平衡易位病例。
