Syncope, defined as a transient loss of consciousness caused by transient global cerebral hypoperfusion, affects 30–40% of humans during their lifetime. Vasovagal syncope (VVS) is the most common cause of syncope, the etiology of which is still unclear. This review summarizes data on the genetics of VVS, describing the inheritance pattern of the disorder, candidate gene association studies and genome-wide studies. According to this evidence, VVS is a complex disorder, which can be caused by the interplay between genetic factors, whose contribution varies from monogenic Mendelian inheritance to polygenic inherited predisposition, and external factors affecting the monogenic (resulting in incomplete penetrance) and polygenic syncope types.

Frequencies of the carriership of alleles and genotypes of functionally important polymorphous loci of some inflammation genes (proinflammatory cytokine genes IL-6, LTA, and TNF; anti-inflammatory cytokine gene TGFB1; and CC chemokine receptor 5 gene CCR5) were analyzed in 199 ethnic Russian patients with myocardial infarction (MI) and in a control group of 142 persons of the same ethnic descent. Complex analysis by the APSampler algorithm revealed associations of MI with the carriership of all polymorphic variants either regarded as individual risk factors (insertion-deletion polymorphism of CCR5 and SNP G252A LTA) or in combination with other alleles or genotypes. The carriership of bi-or triallelic combinations was associated with MI more reliable than the carriership of any subsets: single alleles or allele pairs. The protective triallelic combination d*CCR5 + 252G*LTA + -174C*Il-6 was found to be the most significant (p = 0.0006, OR = 0.23, CI = 0.090–0.56). Separate analysis of genetic susceptibility to MI in men and women demonstrated sexual dimorphism for the CCR5 gene.

The frequencies of alleles and genotypes for ten functionally significant single-nucleotide polymorphisms were determined in the FGA, FGB, APOE, LPL, ACE, and CMA1 genes for Russian ischemic stroke (IS) patients and for a control group of Russians similar in gender and age distribution. The groups showed no significant differences in the frequencies of individual alleles or genotypes for any polymorphism studied. However, complex analysis of genetic susceptibility by the APSampler algorithm demonstrated that carriership of the APOE (−491A) allele predisposed to IS (p = 0.044, OR 3.8, 95% CI 1.0–15.1). Correspondingly, the APOE (−491T/T) genotype was associated with resistance to IS (p = 0.044, OR 0.26, 95% CI 0.07–1.0). The carriership of FGB (−249C) allele together with this genotype enhanced its protective potential, reducing the p value of the combination twofold (OR 0.17, 95% CI 0.04–0.8). Two more protective combinations were identified: biallelic APOE (−427C) + LPL (1595G) and triallelic APOE (−491C) + LPL (1595G) + CMA1 (−1903G). In both cases, p = 0.0052, OR 0.18, and 95% CI 0.05–0.66. Altogether, involvement in the formation of IS risk in Russians was evidenced for alleles of four genes: APOE, FGB, LPL, and CMA1; the APOE involvement was demonstrated for alleles of two polymorphic loci: −491T and −427C. Linkage analysis suggested that these loci were involved in IS resistance independently of each other.

The occurrence of alleles and genotypes of polymorphic region −174G>C of the gene IL6 (rs1800795) in patients of Russian ethnicity with ischemic stroke (200 cases) and in the control of the same ethnicity similar in sex and age (140 control subjects) has been analyzed. Reliable differences were revealed in the carriage frequency of allele IL6*-174G in homozygous and heterozygous form (p = 0.0029, OR = 2.9, 95% CI: 1.4–5.8), which can be considered a risk factor for the development of ischemic stroke, and in the carriage frequencies of protective genotype IL6*-174C/C (p = 0.0029, OR = 0.35, 95% CI: 0.17–0.69), respectively. After the patients and the control subjects were divided by gender character, similar differences were observed only between women with ischemic stroke and those from the control group, and after division by age, they were only revealed in groups with members older than 60 years. Complex analysis of the association of ischemic stroke with the carriage of alleles and genotypes of IL6 SNP-174G>C in combination with SNP 4266A>G (Thr312Ala) of the gene FGA (rs6050) and -249C>T of the gene FGB (rs1800788) revealed protective combinations of IL6*-174C/C + FGA*4266A and IL6*-174C/C + FGB*-249C, which are slightly more reliably associated with ischemic stroke than the one protective genotype IL6*-174C/C and have nearly the same OR value. At the same time, combinations of alternative allele IL6*-174G and the same alleles FGA*4266A or FGB*-249C were revealed that are characterized by a decrease in both the significance level and the OR value as compared with the carriage of one risk allele IL6*-174G. When there is a combined carriage of the allele IL6*-174G with the genotypes FGA*4266A/A, FGB*-249C/C or with combinations of these alleles/genotypes, the neutralizing effect is enhanced. In other words, we observed the association of IL6, FGA and FGB allele combinations with ischemic stroke in which IL6 plays the key role and FGA and FGB have a modulating function. In analyzing the association of the alleles/genotypes of three polymorphic regions with the fibrinogen level in plasma, no reliable difference was revealed.

Vasovagal syncope (VVS) is the most common cause of sudden loss of consciousness. VVS results from cerebral hypoperfusion, due to abnormal autonomic control of blood circulation, leading to arterial hypotension. It is a complex disease, and its development is largely associated with genetic susceptibility. Since abnormal neurohumoral regulation plays an important role in VVS development, we analyzed the association of VVS with polymorphic variants of ADRA1A, ADRB1, HTR1A, ADORA2A, COMT, and NOS3 genes, the products of which are involved in neurohumoral signaling, in patients with a confirmed VVS diagnosis (157 subjects) and individuals without a history of syncope (161 subjects). We were able to identify the associations between VVS and alleles/genotypes ADRA1A rs1048101, ADRB1 rs1801253, ADORA2A rs5751876, and COMT rs4680, as well as NOS3 rs2070744 in biallelic combination with COMT rs4680. Thus, we are the first to observe, within a single study, the role of the genes that encode α- and β-adrenergic receptors, catechol-O-methyltransferase, adenosine receptors and nitric oxide synthase in VVS development. These findings demonstrate that the genes involved in neurohumoral signaling pathways contribute to the formation of a genetic susceptibility to VVS.