No causal link between herpes zoster and ischemic stroke: evidence from Mendelian randomization study

Figures & data

Figure 1. Flowchart of the overall design of the Mendelian randomisation analysis. SNP, single nucleotide polymorphisms.

Figure 2. Overview of the study design and hypotheses for the MR design. Hypothesis 1 suggests that the selected instrumental variables (IVs) for genetic variation are significantly associated with the exposure of interest (HZ); hypothesis 2 suggests that the instrumental IVs for genetic variation are not associated with potential confounders; and hypothesis 3 suggests that genetic variation affects the risk of outcome only through the exposure (HZ), and not through other pathways.

Table 1. Detailed characterisation of GWAS data.

Phenotype	Consortium	Participants (Cases/Controls)	Ancestry	Sample size	PubMed ID or URL
Herpes zoster	FINNGen	4973/362,997	European	367,970	(https://www.finngen.fi/fi)
Stroke	MEGASTROKE	40585/406,111	European	446,696	29531354
Ischemic stroke	MEGASTROKE	34217/406,111	European	440,328	29531354
Cardioembolic stroke	MEGASTROKE	7193/406,111	European	413,304	29531354
Large artery stroke	MEGASTROKE	4373/406,111	European	410,484	29531354
Small vessel stroke	MEGASTROKE	5386/192,662	European	198,048	29531354
Lacunar stroke	ISGC	6030/219,389	European	225,419	33773637

Figure 3. Scatterplot of the genetic association of HZ with stroke and its subtypes. (a) total stroke; (b) ischaemic stroke; (c) large artery stroke; (d) cardioembolic stroke; (e) small vessel stroke; and (f) lacunar stroke. The slope of the straight line indicates the magnitude of causality. Abbreviations: HZ, herpes zoster; SNP, single nucleotide polymorphism; MR, Mendelian randomization.

Figure 4. Forest plot for leave-one-out analysis of genetic associations between HZ and stroke and its subtypes. (a) total stroke; (b) ischaemic stroke; (c) large artery stroke; (d) cardioembolic stroke; (e) small vessel stroke; and (f) lacunar stroke. Bars indicate CI. Abbreviations: HZ, herpes zoster; CI, confidence interval.

Table 2. Causal association of HZ on stroke and its subtypes assessed by 5 MR analysis methods.

Phenotype	nSNPs	F statistic	OR (95%CI)	P
Stroke
IVW	6	23.4	1.04 (0.76,1.79)	0.336
MR-Egger	6		1.17 (0.76,1.79)	0.501
Weighted median	6		1.03 (0.94,1.14)	0.451
Weighted mode	6		1.03 (0.90,1.18)	0.654
Simple mode	6		1.03 (0.90,1.17)	0.672
Ischemic stroke
IVW	6	23.4	1.04 (0.95,1.14)	0.323
MR-Egger	6		1.26 (0.79,1.99)	0.381
Weighted median	6		1.06 (0.94,1.19)	0.286
Weighted mode	6		1.06 (0.92,1.22)	0.416
Simple mode	6		1.06 (0.90,1.26)	0.492
Large vessel ischemic stroke
IVW	7	23.1	1.13 (0.90,1.41)	0.272
MR-Egger	7		1.27 (0.39,4.09)	0.696
Weighted median	7		1.08 (0.81,1.45)	0.575
Weighted mode	7		1.03 (0.73,1.45)	0.852
Simple mode	7		1.01 (0.67,1.52)	0.948
Cardioembolic ischemic stroke
IVW	6	23.4	1.02 (0.85,1.21)	0.816
MR-Egger	6		0.44 (0.17,1.14)	0.168
Weighted median	6		1.03 (0.82,1.30)	0.743
Weighted mode	6		1.08 (0.81,1.45)	0.589
Simple mode	6		1.08 (0.81,1.44)	0.589
Small vessel ischemic stroke
IVW	7	23.1	1.14 (0.93,1.40)	0.195
MR-Egger	7		2.16 (0.65,7.18)	0.260
Weighted median	7		1.07 (0.83,1.38)	0.554
Weighted mode	7		1.06 (0.80,1.42)	0.660
Simple mode	7		1.08 (0.82,1.42)	0.595
Lacunar stroke
IVW	5	22.8	1.19 (0.96,1.47)	0.097
MR-Egger	5		2.42 (0.44,13.15)	0.379
Weighted median	5		1.27 (0.97,1.65)	0.073
Weighted mode	5		1.28 (0.92,1.78)	0.210
Simple mode	5		1.28 (0.91,1.79)	0.220

*nSNPs, number of single nucleotide polymorphisms; OR, odds ratio; CI, confidence interval.

Table 3. Sensitivity analysis of genetically predicted HZ to stroke detailed characterisation of GWAS data.

Outcome	Heterogeneity tests		Horizontal pleiotropy test		IVW-RE
	Methods	Cochran’sQ (P)	MR-Egger intercept (P)	P_pleiotropy*	OR (95%CI)	P
Stroke	MR-Egger	0.54 (0.96)	−1.33E–02(0.60)	0.97	1.17(0.76–1.79)	0.501
	IVW	0.86 (0.97)			1.04(0.95–1.13)	0.336
IS	MR-Egger	1.16 (0.88)	−2.08E–02(0.46)	0.89	1.26(0.79–1.99)	0.381
	IVW	1.80 (0.87)			1.04(0.95–1.14)	0.323
LAS	MR-Egger	2.51 (0.77)	−1.35E–02(0.84)	0.84	1.27(0.39–4.09)	0.696
	IVW	2.55 (0.86)			1.13(0.90–1.41)	0.272
CES	MR-Egger	1.18 (0.88)	9.19E–02(0.15)	0.55	0.44(0.17–1.14)	0.168
	IVW	4.24 (0.51)			1.02(0.85–1.21)	0.816
SVS	MR-Egger	6.56 (0.25)	−7.18E–02(0.33)	0.37	2.16(0.65–7.18)	0.260
	IVW	8.05 (0.23)			1.14(0.93–1.40)	0.195
LS	MR-Egger	1.91 (0.59)	−7.73E–02(0.46)	0.64	2.42(0.44–13.15)	0.379
	IVW	2.59 (0.62)			1.19(0.96–1.47)	0.097

*MR-PRESSO Global Test; IS, ischemic stroke; LAS, great artery apoplexy; SVS, small vessel stroke; CES, cardiac embolic stroke; CI, confidence interval; IVW-FE, inverse weighted variance (fixed effects model).

Data availability statement

Making data available in publicly accessible repositories.

The data provided in this study are publicly available in the FinnGen Consortium [https://www.finngen.fi/en], the MEGASTROKE Consortium, and the IEU OpenGWAS database [https://gwas.mrcieu.ac.uk/].