GJA1 gene variations in sudden unexplained nocturnal death syndrome in the Chinese Han population
Introduction
Sudden unexplained nocturnal death syndrome, first described as the term of “SUNDS” among South Asian immigrants in the USA [1], is characterized by sudden unexplained death occurred during sleep in ostensibly healthy people, most of whom are young males in age 20–50 years old [2]. Standard forensic autopsy, histopathology examination, toxicological analysis, and death-scene investigation show no identifiable morphological changes to explain the underlying cause of death. SUNDS is prevalent predominantly in Thailand, Philipines, Japan, and southern China of southeast Asia [2], [3], [4], and was called with different synonyms according to specific countries, such as “Lai Tai” in Thailand [2], [5], “Bangungut” in the Philippines [3], [6], “pokkuri death syndrome” in Japan [4], and “sudden manhood death syndrome” in China [7], [8]. The annual incidence of SUNDS in southern China has been reported to be as 1–3 per 100,000 people most of which are young males in age 21–40 years old [7], [9], [10]. Because of the huge population, the amount of SUNDS victims may reach over 1000 per year in Southern China by estimation.
It’s generally considered that potential fatal and inherited arrhythmias play an important role in the pathogenesis of SUNDS [11]. Cardiac ion channel coding genes were first linked to congenital and acquired arrhythmia diseases like Brugada syndrome (BrS) and long QT syndrome (LTQS). Previous studies of our research group have also confirmed that such genes as SCN5A, SCN1B, KCNQ1, and RYR2 were related to SUNDS, revealing that arrhythmia-associated cardiac ion channel mutations might account for 10–15% of Chinese SUNDS victims [12], [13], [14]. Nevertheless, the genetic cause of over 80% of SUNDS remains unclear.
Connexin 43 (CX43) protein (also gap junction protein alpha 1, protein product of GJA1 gene) acts as one kind of protein subunits to constitute the gap junction (GJ) channel, which provides an important pathway for intercellular communication of ions and metabolites between adjacent cells [15], [16], [17]. GJ channels constitute most of low resistance channels on the cardiac muscle cells and play a major role in the myocardium to enable the cardiac electrical coupling function of myocardial cells [18], [19].
GJA1 gene variations may be associated to potential fatal arrhythmias and increase the risk of sudden cardiac death. Some researches confirmed a connection between GJA1 gene variations and sudden infant death syndrome (SIDS) as well as sudden cardiac death [20], [22]. In this study, we aimed to determine plausible related variants of GJA1 gene through DNA sequencing and genotype analysis, thus to study the possible contributing role of GJA1 gene in the occurrence of SUNDS.
Section snippets
Study population
124 sporadic SUNDS cases diagnosed from 2005 to 2014 by the Department of Forensic Pathology, Zhongshan School of Medicine, Sun Yat-sen University were collected. The inclusion criteria for SUNDS were as follows as we previously reported [7], [9], [12], [13], [14]: (1) a southern Chinese Han male greater than or equal to 15 years old; (2) apparently healthy without any previously significant disease; (3) prior to experiencing a sudden unexpected death during night sleep; (4) negative
Detected GJA1 gene variants in Chinese sporadic SUNDS cases
In this study, one homozygous variant c.169C > T and one heterozygous SNP c.624C > T (rs530633057) were determined (shown in Table 2). The homozygous variant c.169C > T was a newly discovered non-synonymous variant (the sequencing chromatogram shown in Fig. 1) which was absent in 250 reference alleles in the healthy controls. No information of this variant were reported in the Ensembl database (http://asia.ensembl.org/Homo_sapiens/Gene/Variation_Gene/) or the Exac database (//exac.broadinstitute.org/gene/
Discussion
GJ channels consist of closely packed pairs of transmembrane connexons, through which small molecules as well as ions diffuse from a cell to a neighboring cell [24]. Six connexin oligomers on a cell form half-intercellular channels (called connexons), which interact across a narrow extracellular space (the “gap”) with half-intercellular channels on adjacent cells to form a complete intercellular channel [24]. The sequences of the two extracellular loops are well conserved and three conserved
Conclusion
This study is the first to investigate the GJA1 gene variation in SUNDS cases in the Chinese Han population. Our study determined a novel nonsense variant of GJA1 that is restricted to SUNDS cases. The detected variant would decrease the expression of CX43 GJ channels thus very likely to cause electrical coupling disorder of cardiac muscle cells and lead to sudden death. The results indicated that GJA1 gene maybe a new susceptibility gene for Chinese SUNDS. Further studies with larger samples
Funding
This study was supported by the National Natural Science Foundation of China (grants 81430046).
Competing financial interests
The authors declare no competing financial interests.
Author contributions
J.C. designed the study. Q.W. performed the experiment and wrote the manuscript; J.C. revised the manuscript. Y.W., L.Z., S.T., and J.Z. collected the samples; Q.W., Y.W., L.Z., S.T., and J.C. analyzed the data.
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