Single Nucleotide Polymorphisms Associated With Motor Recovery in Patients With Nondisabling Stroke: GWAS Study

Abstract

Background and objectives: Despite notable advances in genetic understanding of stroke recovery, most studies focus only on candidate genes. To date, only 2 genome-wide association studies (GWAS) have focused on stroke outcomes, but they were limited to the modified Rankin Scale (mRS). The mRS maps poorly to biological processes. Therefore, we performed a GWAS to discover single nucleotide polymorphisms (SNPs) associated with motor recovery poststroke.

Methods: We used the Vitamin Intervention for Stroke Prevention (VISP) data set of 2,100 genotyped participants with nondisabling stroke. We included only participants who had motor impairment at randomization. Participants with a recurrent stroke during the trial were excluded. Genotyped data underwent strict quality control and imputation. The GWAS used logistic regression models with generalized estimating equations to leverage the repeated NIH Stroke Scale motor score measurements spanning 6 time points over 24 months. The primary outcome was a decrease in the motor drift score of ≥1 vs <1 at each time point. Our model estimated the odds ratio (OR) of motor improvement for each SNP after adjusting for age, sex, race, days from stroke to visit, initial motor score, VISP treatment arm, and principal components.

Results: A total of 488 (64%) participants with a mean (SD) age of 66 ± 11 years were included in the GWAS. Although no associations reached genome-wide significance (p < 5 × 10^-8), our analysis detected 115 suggestive associations (p < 5 × 10^-6). Notably, we found multiple SNP clusters near genes with plausible neuronal repair biology mechanisms. The CLDN23 gene had the most convincing association with rs1268196-T as its most significant SNP (OR 0.32; 95% CI 0.21-0.48; p value 6.19 × 10^-7). CLDN23 affects blood-brain barrier integrity, neurodevelopment, and immune cell transmigration.

Discussion: We identified novel suggestive genetic associations with the first-ever motor-specific poststroke recovery GWAS. The results seem to describe a distinct stroke recovery phenotype compared with prior genetic stroke outcome studies that use outcome measures, such as the mRS. Replication and further mechanistic investigation are warranted. In addition, this study demonstrated a proof-of-principle approach to optimize statistical efficiency with longitudinal data sets for genetic discovery.

Figure 1. Nonlinear Probability of Motor Improvement Over Time

The nonlinear relationship of the mean probability of motor improvement for each follow-up time point since study randomization. The green and orange line segments highlight the notable change in slope from 1- to 6-month visits to 6- to 24-month visits after randomization. The nonlinear relationship of motor improvement time is well known from chronic stroke rehab trials of the upper extremity.

Figure 2. Genome-wide Association Study Manhattan Plot of Poststroke Motor Recovery

This Manhattan plot shows each SNP and its -log10 (p value) associated with poststroke motor improvement. None of the SNPs reached genome-wide significance (above the red line). However, 115 SNPs had suggestive associations (above the blue line), with 2 right under the red line. The most convincing genetic locus is the large spike in chromosome 8, near the Claudin 23 gene. This gene affects the blood-brain barrier and immune cell transmigration. Red dotted line marks the Bonferoni threshold of -log10 (5e-8). Blue dotted line marks the suggestive threshold of -log10 (5e-6). SNP = single nucleotide polymorphism.

Figure 3. Suggestive Genetic Loci of Interest and Their Linkage Disequilibrium

Panel plot of Locus Zoom figures (A–D) corresponding to genetic loci of interest. The colors refer to the correlation of each SNP to the top SNP in each panel, with red having an r² ≥ 0.80. (A) Genetic locus near the CLDN23 gene on chromosome 8. (B) Genetic locus within the PTPRD gene on chromosome 9. (C) Genetic locus within the RIMBP2 gene on chromosome 12. (D) Genetic locus between the RTTN and SOCS6 genes on chromosome 18. SNP = single nucleotide polymorphism.

Figure 4. CLDN23 Associations Have Larger Effect Sizes Within 6 Months of Enrollment vs Later

Shows the estimates and 95% confidence intervals of the interaction of the study time points 1–6 months vs 6–24 months with each suggestive SNP found in chromosome 8. Interestingly, the interaction estimates of many SNPs seem to straddle one, with SNP estimates at 1–6 months having greater odds of motor recovery. In comparison, SNP estimates at 6–24 months have less odds of motor recovery. SNP = single nucleotide polymorphism

Figure 5. CLDN23 Associations Are Robust to Time From Stroke to Study Enrollment

Odds ratios and 95% confidence intervals of motor drift score improvement from the interaction early vs late poststroke randomization by SNP in chromosome 8. The odds ratios estimates for early vs late do not have a discernible pattern or consistency. SNP = single nucleotide polymorphism.