Department of Nephrology, The Affiliated Qingdao Municipal Hospital of Qingdao University, No.5 Donghai Middle Road, 266071, Qingdao, People's Republic of China.
Central Laboratory, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China.
Endocrine. 2019 Jun;64(3):708-718. doi: 10.1007/s12020-019-01856-6. Epub 2019 Feb 21.
Bartter syndrome type I (BS1) has been rarely reported in large groups. On the other hand, the phenomenon of exon skipping, in which exonic mutations result in abnormal splicing, has been reported to be associated with various diseases. Specifically, mutations that result in the disruption of exonic splicing enhancers (ESEs) and/or the creation of exonic splicing silencers (ESSs) can promote exon skipping. However, the aberrant exon skipping caused by an exonic variant in such splicing regulatory elements (SREs) sequences has never been reported in the causal gene of SLC12A1 in BS1.
We analyze the variants in nine Chinese families with BS1, including eight with antenatal BS (aBS) and one presenting as classical BS (cBS), by next-generation sequencing. Then we used bioinformatics programs to analyze all these variants found in this study and identify candidate mutations that may induce exon skipping. Furthermore, the effects of identified variants were classified according to the 2015 American College of Medical Genetics and Genomics (ACMG) standards and guidelines.
Fifteen different variants of SLC12A1 gene were identified, including 11 novel ones. Two of the nine probands were homozygotes, the rest seven ones were compound heterozygotes. One candidate variant (c.1435C>G), not only significantly reduced ESEs scores but also markedly increased ESSs scores, were further investigated by mini-gene splicing assay, and found this single-nucleotide substitution causes abnormal splicing in vitro (exclusion of exon 11). Finally, among 15 variants, 9, 3, and 3 were classified as "pathogenic variants", "likely pathogenic variants", "variants with uncertain significance", respectively.
These data would enrich the human gene mutation database (HGMD) and would provide valuable references to the genetic counseling and diagnosis of BS1 for Chinese population. Additionally, our results suggest that aberrant exon skipping is one previously unrecognized mechanism by which an exonic variant in SLC12A1 can lead to BS1.
巴特综合征 1 型（BS1）在大型群组中很少见。另一方面，外显子跳跃现象已被报道与各种疾病相关，这种现象是指由于外显子突变导致异常剪接。具体而言，导致外显子剪接增强子（ESEs）和/或外显子剪接沉默子（ESSs）破坏的突变可促进外显子跳跃。然而，在 BS1 的 SLC12A1 致病基因中外显子变异导致的异常外显子跳跃从未被报道过。
我们通过下一代测序分析了 9 个中国 BS1 家庭的变异，包括 8 个产前 BS（aBS）和 1 个经典 BS（cBS）。然后，我们使用生物信息学程序分析了本研究中发现的所有这些变体，并确定了可能导致外显子跳跃的候选突变。此外，根据 2015 年美国医学遗传学与基因组学学会（ACMG）标准和指南，对鉴定的变异进行分类。
鉴定出 SLC12A1 基因的 15 种不同变体，包括 11 种新变体。9 个先证者中有 2 个是纯合子，其余 7 个是复合杂合子。进一步通过迷你基因剪接试验研究了 9 个先证者中的一个候选变体（c.1435C>G），该变体不仅显著降低了 ESEs 评分，而且显著增加了 ESSs 评分，发现该单核苷酸替换导致体外异常剪接（11 号外显子缺失）。最后，在 15 种变体中，9、3 和 3 种分别被归类为“致病性变体”、“可能致病性变体”和“意义不确定的变体”。
这些数据将丰富人类基因突变数据库（HGMD），并为中国人群的 BS1 遗传咨询和诊断提供有价值的参考。此外，我们的结果表明，异常外显子跳跃是 SLC12A1 中一个外显子变异导致 BS1 的一种先前未被认识的机制。
