Molecular study on Nijmegen breakage sybdrome

共济失调性毛细血管扩张症的ATM基因，对于AT的表型表达仍然是个谜，ATIKE基因可能有助于理解这一机制。奈梅根断裂综合征(NBS)具有与AT完全不同的临床特征，因为NBS患者没有甲胎蛋白升高、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，染色体不稳定、辐射敏感性增加和细胞周期检查点异常等细胞生物学表现与AT相似，表明两种综合征都存在相同的途径受损。尽管P53的诱导具有剂量依赖性，但诱导的起始时间延迟，且照射后数小时的最大P53低于正常细胞。因此，NBS淋巴母细胞对P53的诱导介于正常细胞和AT细胞之间，与AT细胞相比，NBS对细胞杀伤的辐射敏感性较低。然而，通过与NBS细胞和AT细胞的融合细胞的互补分析，证实了NBS和AT的不同的潜在基因。为了鉴定携带NBS基因的染色体，我们将单个人染色体或其片段通过微细胞导入NBS建立的细胞中，并根据辐射敏感性进行互补分析。只有含有人染色体8q21-23区域的杂交细胞才恢复了辐射抗性。此外，对一个有血缘关系的患者家系的单倍体DNA分析强烈表明D8S1811附近的1-2 cM DNA区域是候选基因，这些结果为下一步的基因克隆和了解AT-ike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.