Van Dyke D L, Weiss L, Logan M, Pai G S
Am J Hum Genet. 1977 May;29(3):294-300.
Karyotyping revealed three cell lines in a boy with mental retardation and few other abnormalities. Thirty cells exhibited a normal karyotype, and 54 had an extra acrocentric chromosome of E group size with satellites on the long and short arms. The remaining 20 cells each had, in addition to the first marker (M1), a second tiny bisatellited chromosome (M2). C-banding demonstrated that both markers were dicentric. G-, C-, and Q-banding and satellite association data were consistent with the markers having originated from chromosome 15 material. We propose that M1 was formed from a meiotic breakage and a chromatid fusion in the proximal long arms of an acrocentric pair. This would have produced a symmetrical isodicentric chromosomes, plus one or two acentric fragments. M2 then could have resulted from a dicentric bridge-break-synthesis-reunion phenomenon. This model of abnormal meiotic exchange can be generalized to encompass the formation of other dicentric isochromosome cases of isochromosome X.
核型分析显示，一名患有智力障碍且伴有其他一些轻微异常的男孩存在三种细胞系。30个细胞呈现正常核型，54个细胞有一条额外的E组大小的近端着丝粒染色体，其长短臂均带有随体。其余20个细胞除了第一条标记染色体（M1）外，各自还有一条微小的双随体染色体（M2）。C显带显示两条标记染色体均为双着丝粒。G显带、C显带、Q显带以及随体联合数据均表明这些标记染色体源自15号染色体物质。我们推测M1是由近端着丝粒染色体对的长臂近端减数分裂断裂和染色单体融合形成的。这会产生一条对称的等臂双着丝粒染色体，外加一或两个无着丝粒片段。然后M2可能是由双着丝粒桥断裂-合成-重聚现象导致的。这种异常减数分裂交换模型可以推广到涵盖其他双着丝粒等臂染色体病例，如X等臂染色体。
