RNF213 Is Associated with Intracranial Aneurysms in the French-Canadian Population

Abstract

Intracranial aneurysms (IAs) are the result of focal weakness in the artery wall and have a complex genetic makeup. To date, genome-wide association and sequencing studies have had limited success in identifying IA risk factors. Distinct populations, such as the French-Canadian (FC) population, have increased IA prevalence. In our study, we used exome sequencing to prioritize risk variants in a discovery cohort of six FC families affected by IA, and the analysis revealed an increased variation burden for ring finger protein 213 (RNF213). We resequenced RNF213 in a larger FC validation cohort, and association tests on further identified variants supported our findings (SKAT-O, p = 0.006). RNF213 belongs to the AAA+ protein family, and two variants (p.Arg2438Cys and p.Ala2826Thr) unique to affected FC individuals were found to have increased ATPase activity, which could lead to increased risk of IA by elevating angiogenic activities. Common SNPs in RNF213 were also extracted from the NeuroX SNP-chip genotype data, comprising 257 FC IA-affected and 1,988 control individuals. We discovered that the non-ancestral allele of rs6565666 was significantly associated with the affected individuals (p = 0.03), and it appeared as though the frequency of the risk allele had changed through genetic drift. Although RNF213 is a risk factor for moyamoya disease in East Asians, we demonstrated that it might also be a risk factor for IA in the FC population. It therefore appears that the function of RNF213 can be differently altered to predispose distinct populations to dissimilar neurovascular conditions, highlighting the importance of a population's background in genetic studies of heterogeneous disease.

Figure 1

Six Pedigrees with 26 IA-Affected Individuals from the Initial Cohort

Figure 2

Matrix of Pairwise F_ST of RNF213 across Worldwide Populations F_ST was calculated for RNF213 common variants from the Omni chip (A) and functional variants from exome sequencing and (B) between each two populations. FC_CTRL and FC_IA are the FC control cohort and the IA cohort, respectively; other populations are indicated by the three-letter codes used by 1KGP. The allele distributions of RNF213 common SNPs vary among populations, suggesting the existence of genetic drift. Among others, there is a big difference in the allelic distributions of RNF213 functional variants between Asians and FC populations.

Figure 3

ATPase Activity of the Wild-Types, Variants, and LOF Controls of the Two AAA+ Domains of RNF213 Box-and-whisker plot showing ATPase activity measured as nmol of free-phosphate release per mg protein per minute. A1WT and A2WT are the wild-types of the first and second AAA+ modules, respectively; A1M and A2M are the p.Arg2438Cys and p.Ala2826Thr variants, respectively. A1WA, A1WB, A2WA, and A2WB are four LOF controls (p. Lys2426Ala, p. Glu2488Ala, p. Lys2775Ala, and p. Glu2845Ala, respectively) located in the walker A and B domains of the first and second AAA+ modules. The results were generated by eight ATPase assays from two independent cell cultures; each sample is measured in duplicate. Boxes show the interquartile range, and whiskers show maximum and minimum measurements.

Figure 4

Meta-analysis of Two RNF213 Studies in Different Populations Forest plot of Moteki et al. and the current study. Result show significantly more RNF213 mutations in FC IA-affected individuals (Cochran-Mantel-Haenszel test: p < 0.0001). Error bars represent confidence intervals, shown on the right.

Figure 5

RNF213 Rare Functional Variants Exclusively Found in IA- and MMD-Affected Individuals Adapted from Cecchi et al. and Koizumi et al. 14 variants found in the current study are marked in red, variants reported in Moteki et al. are marked in blue, MMD variants reported in Cecchi et al. are marked in black, and MMD variants found in other studies are marked in gray. The results show that FC IA-affected individuals harbor more deleterious mutations in the AAA+ domains than other populations do.