Kerem Eitan
Department of Pediatrics and Cystic Fibrosis Center, Hadassah University Hospital, Mount Scopus, Jerusalem, Israel.
Curr Opin Pulm Med. 2004 Nov;10(6):547-52. doi: 10.1097/01.mcp.0000141247.22078.46.
The purpose of this review is to summarize the recent approaches using mutation-specific therapy to correct the genetic defect according to the molecular mechanism by which the mutation causes the defects in cystic fibrosis transmembrane conductance regulator (CFTR). Premature stop mutations (class I mutations) account for 5 to 10% of the total mutant alleles in cystic fibrosis patients, and in certain subpopulations the incidence is much higher.
The aminoglycoside antibiotics can suppress premature termination codons by permitting translation to continue to the normal termination of the transcript. The susceptibility to suppression by aminoglycosides depends on the stop codon itself and on the sequence context surrounding it. In vitro studies in cell lines expressing stop mutations and in mice have shown that aminoglycosides caused a dose-dependent increase in CFTR expression and restored functional CFTR to the apical membrane. Clinical studies also provided evidence that the aminoglycoside gentamicin can suppress these CFTR premature stop mutations in affected patients. A recent double-blind, placebo-controlled, crossover study has demonstrated restoration of CFTR function by topical application of gentamicin to the nasal epithelium of cystic fibrosis patients carrying stop mutations. In 21% of the patients there was a complete normalization of all the electrophysiologic abnormalities caused by the CFTR defect, and in 68% there was restoration of either chloride or sodium transport. Furthermore, immunohistochemical staining to the C-terminal part of the CFTR was demonstrated via peripheral staining for CFTR in scraped nasal epithelial cells of patients carrying stop mutations. Inconsistent results were reported regarding the required level of corrected CFTR that has to be reached to achieve normal function. Achieving CFTR activity of 10 to 35% might be needed to prevent significant pulmonary morbidity.
It is as yet unknown how much corrected mutant CFTR must reach the apical membrane to induce a clinically relevant beneficial effect. The future goal is to maximize the effect of stop-codon supressors on CFTR while minimizing side effects, but further studies must be performed to find a safer compound that may be administered in small children from the time of diagnosis.
本综述旨在总结近期利用突变特异性疗法根据突变导致囊性纤维化跨膜传导调节因子（CFTR）缺陷的分子机制来纠正基因缺陷的方法。过早终止突变（I类突变）占囊性纤维化患者总突变等位基因的5%至10%，在某些亚群体中发生率更高。
氨基糖苷类抗生素可通过允许翻译继续至转录本正常终止来抑制过早终止密码子。对氨基糖苷类抑制的敏感性取决于终止密码子本身及其周围的序列背景。在表达终止突变的细胞系和小鼠中的体外研究表明，氨基糖苷类导致CFTR表达呈剂量依赖性增加，并将功能性CFTR恢复至顶膜。临床研究也提供了证据表明氨基糖苷类庆大霉素可在受影响患者中抑制这些CFTR过早终止突变。最近一项双盲、安慰剂对照、交叉研究表明，对携带终止突变的囊性纤维化患者鼻上皮局部应用庆大霉素可恢复CFTR功能。在21%的患者中，由CFTR缺陷引起的所有电生理异常完全恢复正常，68%的患者恢复了氯或钠转运。此外，通过对携带终止突变患者刮取的鼻上皮细胞中CFTR的外周染色，证实了对CFTR C末端部分的免疫组织化学染色。关于达到正常功能所需的校正CFTR水平，报道结果不一致。可能需要达到10%至35%的CFTR活性以预防显著的肺部疾病。
目前尚不清楚校正后的突变CFTR必须有多少到达顶膜才能产生临床相关的有益效果。未来的目标是在使终止密码子抑制剂对CFTR的作用最大化的同时，将副作用最小化，但必须进行进一步研究以找到一种更安全的化合物，可在幼儿诊断时给药。
