Molecular study on Nijmegen breakage sybdrome

ATM基因是共济失调毛细血管扩张的基础基因，对ATM的表型表达和AT样基因的表达可能有助于理解这一机制。奈梅根断裂综合征（NBS）的临床特征与AT有很大不同，因为NBS患者不表现为甲胎蛋白升高、小脑性共济失调或毛细血管扩张，但确实有小头畸形和生长迟缓。然而，细胞生物学的发现，如染色体不稳定、辐射敏感性增加和细胞周期检查点异常，与AT相似，表明同一途径在两种综合征中受损。NBS和AT在辐照后p53诱导中有相似之处。虽然p53的诱导是剂量依赖性的，但诱导的开始是延迟的，照射后数小时p53的最大值低于正常细胞。因此，p53在NBS淋巴细胞中的诱导介于正常细胞和AT细胞之间，这与NBS对细胞杀伤的轻微辐射敏感性相比AT细胞。然而，通过NBS细胞和AT细胞的融合细胞的互补实验，证实了NBS和AT的潜在基因不同。为了鉴定携带NBS基因的染色体，我们将一条人类染色体或其片段通过微细胞导入NBS建立的细胞，并基于辐射敏感性检测其互补性。只有含有人类染色体8q21-23区域的杂交细胞恢复了辐射抗性。此外，对一个有血缘关系的患者家族的单倍体DNA分析强烈提示D8S1811周围1-2 cM的DNA区域是候选位点。这些结果为下一步的基因克隆和了解at - like基因的功能提供了有用的信息。

ATM underlying gene for Ataxia Telangiectasia, is still mysterious for the phenotypic expression of AT and AT Iike gene could be helpful to understand this mechanism. Nijmegen Breakage Syndrome (NBS) has quite different clinical features from AT,since patients with NBS do not show elevation of alpha-fetoprotein, cerebellar ataxia, or telangiectasia but do have microcephaly and growth retardation. However, the cell-biological findings, such as chromosome instability, increased radiation sensitivity and abnormal cell cycle check point, resemble those in AT,suggesting that the same pathway is impaired in both syndromes.Similarity between NBS and AT was observed in p53 induction after irradiation. Although the induction of p53 was dose-dependent, the onset of induction was delayd and the maximum p53 at several hrs after irradiation was lower than that of normal cells. Consequently, p53 induction in NBS Iymphoblasts was intermediate between normal cells and AT cells, and this corresponds to a mild radiation sensitivity of NBS to cell killing in comparison with AT cells. However, different underlying genes for NBS and AT were confirmed by complementation assay using fused cells with NBS cells and AT cells. To identify the chromosome carrying NBS gene, we introduced a single human chromosome or their fragments into NBS established cells through microcell and assayd the complementation based on radiation sensitivity. Only hybrid cells containing a human chromosome region 8q21-23 was restored the radiation resistance. Furtermore, the haploid DNA analysis of a patient family with consanguinity strongly suggests the 1-2 cM DNA region around D8S1811 as the candidate locus.These results are useful information for the next step of gene cloning and understanding of AT-Iike gene function.