Cohen O, Cans C, Cuillel M, Gilardi J L, Roth H, Mermet M A, Jalbert P, Demongeot J
Constitutional Genetic Laboratory, Medical School of Grenoble, France.
Hum Genet. 1996 May;97(5):659-67. doi: 10.1007/BF02281879.
Reciprocal translocations (rcp) are among the most common constitutional chromosomal aberrations in man. Using a European database of 1574 families carrying autosomal rcp, a cartographic study was done on the breakpoints involved. The breakpoints are non-randomly distributed along the different chromosomes, indicating "hot spots". Breakpoints of rcp that result in descendants that are unbalanced chromosomally at birth are more frequent in a distal position on chromosomal arms, and 65% of them are localised in R-bands. Among the R-bands, bands rich in GC islands and poor in Alu repetitive sequences are more frequently the site of breakpoints, as well as bands that include a fragile site. This result suggests that the variation in degree of methylation in GC islands could be involved in chromosomal breakage and hence in chromosomal rearrangements. The heterogeneity of the human chromosomal structure has been demonstrable by metaphase banding techniques since 1970. In contrast to G-bands, R-bands are sites of high gene concentration (Korenberg et al. 1978), are relatively rich in cytosine plus guanine (GC), and in Alu repetitive DNA sequences (Korenberg and Rykowski 1988). More recently Holmquist (1992) has proposed four types of R-bands, depending on their relative richness in GC and Alu DNA sequences. R-bands rich in GC correspond almost exactly to T-bands (Dutrillaux 1977). They contain 65% of all genes while they represent only 15% of the genome (Holmquist 1992). The aim of this study is to analyse the distribution of the breakpoints along chromosomes from a European database of autosomal rcp in order to relate it to the specificity of different chromosomal regions.
相互易位（rcp）是人类中最常见的染色体结构畸变之一。利用一个包含1574个携带常染色体相互易位的家庭的欧洲数据库，对所涉及的断点进行了图谱研究。断点在不同染色体上呈非随机分布，表明存在“热点”。导致后代出生时染色体不平衡的相互易位断点在染色体臂的远端位置更为常见，其中65%位于R带。在R带中，富含GC岛且Alu重复序列较少的带以及包含脆性位点的带更常成为断点所在位置。这一结果表明，GC岛甲基化程度的变化可能与染色体断裂有关，进而与染色体重排有关。自1970年以来，中期显带技术已证实人类染色体结构的异质性。与G带不同，R带是基因高度集中的区域（科伦伯格等人，1978年），相对富含胞嘧啶加鸟嘌呤（GC）以及Alu重复DNA序列（科伦伯格和里科夫斯基，1988年）。最近，霍尔姆奎斯特（1992年）根据其在GC和Alu DNA序列中的相对丰富程度提出了四种类型的R带。富含GC的R带几乎与T带完全对应（迪特里洛，1977年）。它们包含所有基因的65%，而仅占基因组的15%（霍尔姆奎斯特，1992年）。本研究的目的是分析来自常染色体相互易位欧洲数据库的染色体上断点的分布情况，以便将其与不同染色体区域的特异性联系起来。
