心肌生物钟基因变异与SUNDS发病机制的新探索

The genetic cause of sudden unexplained nocturnal death syndrome （SUNDS）in part cases was elucidated in previous studies by our group. Currently, the etiology of about 80% of SUNDS cases remains unknown. But recently, a breakthrough in the research of circadian clocks showed that circadian rhythm genes govern cardiac repolarization and arrhythmogenesis (cardiac electrophysiological stabilities), just like circadian rhythm genes control sleep, metabolism, and respiration. We hypothesize that there are numerous pathogenic variants of circadian rhythm genes in SUNDS due to its prominent circadian characters (sudden cardiac electical instability during nocturnal sleep). To break through the bottleneck of etiological research on SUNDS and to explore opportunities with international researchers in seeking pathogenic variants in SUNDS, we plan to perform the following research: Based on the previous database (diseases spectrum) of cardiac ion channel gene variants that we established, variants in the circadian clock genes of SUNDS victims will be screened to find the plausible molecular etiology of SUNDS. Cellular electrophysiological studies will be performed of these variants in human induced pluripotent stem cell derived cardiomyocytes to identify if they are pathogenic mutations. Mutations with obvious functional phenotypes will be chosen to make transgenic mice that address the mechanisms by which SUNDS occur in an animal model of disease. Through these studies, we expect to find new susceptible SUNDS genes, enlarge the database of molecular pathology of SUNDS, and provide scientific evidences for elucidating the mechanisms of SUNDS, improving its molecular pathological diagnosis, and exploring prevention methods.

我们业已阐明了部分青壮年不明原因夜间睡眠中猝死综合征（SUNDS）的分子病因，但至今仍有约80%的SUNDS难于捕获到原发病因。新近的重大科学发现揭示心肌电稳定性与睡眠、代谢、呼吸等生物节律一样受生物钟基因的复杂调控。我们认为，具有显著生物节律特征（猝死于夜间睡眠，突发心电失稳）的SUNDS中应蕴含丰富的生物钟基因致病突变信息。为突破SUNDS病因研究瓶颈，与国际同行抢占疾病信息发掘的先机，拟在前期建立的心脏离子通道基因病变谱的基础上，发掘SUNDS生物钟基因的遗传变异资源，筛选出可疑分子病因；在人源性诱导多能干细胞分化心肌中研究突变体的细胞电生理功能，确立致病突变体；在转基因小鼠动物整体水平探索功能表型显著异常的突变体的致病机制。籍此，以期发现SUNDS新的易感基因，丰富SUNDS的分子病变谱，为进一步解析SUNDS的发生机制、完善其分子病理学诊断、探寻其综合防治方法提供科学依据。

本项目首次从生物钟节律角度探寻了中国人青壮年不明原因夜间睡眠中猝死（SUNDS）的流行病学特征及分子病因。利用丰富的病例资源，我们开展了持续的流行病学监测，研究表明南粤地区SUNDS的发生数较恒定，维持在1-2人/10万/年；来自海南、云南、香港、台湾的人群在南粤地区可能具有更高的SUNDS猝死风险；SUNDS异常高发于3-6月份，以夜间睡眠中猝死、凌晨或白天被发现死亡为主要表现，死亡高峰季节与雨季气温剧变期一致，论证了SUNDS猝死的发生存在明显的生物钟节律。在长QT综合征（LQTS，以白天、运动中猝死为主要生物节律特点）易感基因NOS1AP多态性变异与SUNDS的相关性研究中发现，rs12567209少见等位基因A、rs10918594, rs12143842, rs16847548, rs12567209 及rs10494366等五个多态位点的单倍型GCTAT及GTCGT在SUNDS发生中起保护作用；从分子流行病学角度高度提示了SUNDS发生具有静息、睡眠中猝死的生物钟节律，与LQTS为代表的白天、运动中猝死生物节律相区别。在SUNDS分子遗传学研究中，在儿茶酚胺敏感性多形性室速（CPVT）及致心律失常性右室心肌病（ARVC）易感基因RyR2基因的突变热点区未发现致病突变，与猝死密切相关的RyR2多态G1886S与SUNDS的发生无相关；这些结果强烈提示，SUNDS猝死可能与CPVT及ARVC猝死无明显相关，再次论证到SUNDS的发生不具有运动性猝死的生物钟节律特征。在生物钟基因的扫描中，已发现Per3的长度多态性与SUNDS的发生相关，暂未发现Clock、Bmal1、Per1、Per2、Per3、Cry1、Cry2基因的已知致病突变。通过本研究，进一步丰富了SUNDS的病例资源库、流行病学基础数据及生物钟节律相关的分子遗传学研究数据；进一步论证了SUNDS的发生具有明显的生物钟节律，为SUNDS的防治提供了研究基础及科学依据；也为我们下一步探寻SUNDS的分子病因及猝死机制提供了新方向。