Bartram C R, Koske-Westphal T, Passarge E
Ann Hum Genet. 1976 Jul;40(1):79-86. doi: 10.1111/j.1469-1809.1976.tb00166.x.
The frequency of BrdU-induced sister chromatid exchanges (SCE) in cultured lymphocytes from patients with ataxia telangiectasia, Werner syndrome, and xeroderma pigmentosum was normal. The rate was increased in xeroderma pigmentosum following exposure to ultraviolet light and spontaneously raised in the Bloom syndrome. Quadriradial exchanges between homologous chromosomes in Bloom syndrome not only involve sister chromatids but also homologous (non-sister) chromatids. This could result in the formation of recombinant chromosomes and is viewed as a genetically determined form of increased somatic recombination in man. Endoreduplicated metaphases showed 'twin' and 'single' exchanges in a 1:2 ratio. This suggests a comparable frequency of exchanges at both divisions and provides evidence for the polarity of the chromatid subunits and the presence of a single chain of DNA.
共济失调毛细血管扩张症、沃纳综合征和着色性干皮病患者培养淋巴细胞中，溴脱氧尿苷诱导的姐妹染色单体交换（SCE）频率正常。着色性干皮病患者经紫外线照射后该频率增加，而布卢姆综合征患者该频率自发升高。布卢姆综合征中同源染色体之间的四射体交换不仅涉及姐妹染色单体，还涉及同源（非姐妹）染色单体。这可能导致重组染色体的形成，被视为人类体细胞重组增加的一种遗传决定形式。核内复制中期显示“双”交换和“单”交换的比例为1:2。这表明在两个分裂期交换频率相当，并为染色单体亚基的极性和单链DNA的存在提供了证据。
