For the first time, we conducted a two-phases WEWAS on Korean adults with MMD and compared the WES data of these patients with those of disease-free healthy subjects, validating the mutational signal of RNF213. Additionally, potential mutations in GAA and CHMP6 were identified during the discovery and validation phases, as were de novo mutations in MUC4, FGFRL1, PRIM2, and MAP3K9. Intriguingly, WEWAS-driven mutations within the 17q25.3 region, referred to as MARS9, demonstrated an area under the curve between 0.8296 and 0.8380 in predicting MMD development. Nonetheless, no significant mutations associated with angiographic progression were discovered, despite MMD patients with angiographic progression harboring at least five missense mutations in RNF213.
The RNF213 polymorphism within the 17q25 region, notably the p.R4810K (rs112735431) mutation, which has been associated with MMD risk, has been acknowledged as a potential factor for MMD.23–25 Wang et al. (2020) reported that mutation of the “A” allele in p.R4810K was closely associated with early onset of MMD and posterior cerebral artery involvement.25 In the contrary of East-Asia, the R4810K variant of RNF213, which encodes a RING finger and two AAA + domains, was not often found in Caucasian MMD patients. Studies have indicated that carrying the “A” allele for p.R4810K is correlated with early onset of MMD and involvement of the posterior cerebral artery. This variation is less common in Caucasian MMD patients than in East-Asian patients, suggesting a diverse genetic predisposition based on ethnicity.26 In Northern European adults with MMD, WES analysis revealed de novo mutations affecting nitric oxide metabolism but did not reveal the p.R4810K mutation.7 In our study, six out of the ten RNF213 gene missense mutations, p.K1034M, p.V1195M, p.E1272Q, p.D1331G, p.S2334N, and p.R4810K, were found to be genome-wide significant for adult MMD in Koreans. These findings imply that MMD may result from multiple mutations or interactions rather than from a single point mutation, such as p.R4810K. Although certain mutations, such as p.R4810K, were validated in our analysis, further studies are needed to understand the structural role and overall impact of other functional mutations in RNF213.
In addition to RNF213, our research points to significant mutations in two loci, GAA and CHMP6, as additional major contributors to MMD. The missense mutations p.G576S and p.E689K in GAA, identified for the first time in this WEWAS, play a crucial role in producing the acid alpha-glucosidase enzyme, which is pivotal for converting glycogen polymers to glucose in lysosomes. The absence or deficiency of GAA products causes glycogen accumulation and subsequent cellular damage.27 Jia et al. reported that heterozygous mutations in GAA were related to cerebral inflammation in patients with Pompe disease and glycogen storage disease type II.28 However, studies on how GAA affects MMD are rare. Glycogen accumulation caused by GAA deficiency leads to abnormal lysosomes, which impair autophagy.29 Although the relationship between RNF213 variants and autophagic dysfunction is known, autophagic inhibition has been shown to impair endothelial function in human endothelial cells under oxygen–glucose deprivation conditions.30 Youn et al. also reported that autophagic and mitophagic dysfunction in cerebrospinal fluid cells may be related to neurological outcomes in adult MMD patients.31 Based on these findings, we hypothesized that dysfunction due to GAA mutations may damage the cerebral endothelium and cause arterial abnormalities via autophagic impairment, resulting in an abnormal vascular network.
Charged multivesicular body protein 6, CHMP6 is responsible for encoding a chromatin-modifying protein and charged multivesicular body protein. Overexpression of CHMP6–GFP (green fluorescent protein) leads to the accumulation of transferrin receptors (TfRs) in the cytoplasm; TfRs play a crucial role in regulating the cellular iron supply by binding to transferrin.32 Furthermore, elevated levels of ubiquitinated membrane proteins, including the epidermal growth factor receptor, can be observed in cells expressing CHMP6–GFP. An increase in ubiquitinated proteins during endocytosis can potentially harm vascular smooth muscle cells (VSMCs). Dziewulska and Rafalowska (2008) suggested the potential involvement of aberrant ubiquitin-dependent endocytosis of the Notch 3 ligand in the injury of VSMCs in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy.33 Additionally, RNF213 contains a unique class of E3 ubiquitin ligases. Pathogenic mutations in RNF213, which cluster within the composite E3 domain, could lead to abnormal ubiquitination interactions with substrates.34 However, the role of CHMP6 mutations in the development of MMD has not been determined, necessitating further in vivo or in vitro research to elucidate the pathogenesis of CHMP6.
Our WEWAS-drivee models revealed that the MARS of polygenic architecture indicate multiple mutational effects or interactions at regional or chromosomal levels, such as 17q25.3, yielding a diagnostic accuracy exceeding 80% for MMD. Notably, the MARS9 model, which includes nine missense mutations, emphasizes that MMD is closed to a complex disorder rather than a Mendelian disorder. Polygenic risk assessment could prove beneficial for early disease detection and timely intervention, despite inherent challenges such as reduced effectiveness in the general population and reliance on statistical algorithms or existing knowledge.35–37 In addition, polygenic risk contributes to be cost- and time-effective than other alternatives if direct functional mutations can be validated in the other independent group, reducing a cost of unnecessary screening for MMD. Furthermore, drive mutations can contribute to improving an informative strategy by avoiding unnecessary genotyping tests.38 Our MARS models will definitely support a better information in clinical and precision medicines. In addition, the profits of pre-screening by a reliable MARS-based panel is likely to reduce potential side effects such as, for example, unnecessary screening, radiation exposure, overdiagnosis, and neuro-degenerative distress after onset symptoms.39
Our study has several limitations. Primarily, the relatively small size of the datasets may impede the ability to draw definitive conclusions, even though our work represents the largest WES effort in MMD featuring discovery and validation phases, along with comparisons to genetic data from open cohorts. Second, while we identified several mutations in RNF213, GAA, and CHMP6 localized at 17q25.3, unlike the point mutations p.R4810K (RNF213) and p.D54K (CHMP6), LD-associated mutations are thought to influence gene expression rather than cause structural dysfunctions. Consequently, extensive research is needed to explore not only the individual impact of specific mutations but also their interactions and the resultant overall effect on MMD development, which could involve gene or allele-specific expression analysis, transcriptome-wide association studies, or in vivo investigations. Third, while we introduced Korean-specific MARS models for MMD diagnosis prediction, their broad application in the general clinical domain of neurodegenerative diseases necessitates further validation across independent cohorts and various ethnic groups. Finally, the absence of mutations specifically associated with angiographic progression in our study might reflect the limited number of documented patients. Therefore, expanded studies based on a larger cohort of MMD patients experiencing angiographic progression are essential.
We shed light on coding modifiers and mutations associated with adult MMD in the two-stage WES-based study, offering valuable insights into its genetic underpinnings. Our best-fitting MARS approach proposed herein holds promise for improving MMD diagnosis and understanding the potential for disease development. Further in-depth applications will be addressed to confirm our findings, to evaluate gene-gene or gene-environment interactions, and to determine the clinical relevance to genetic mechanisms for understanding MMD etiology.
Data and resource availability
The data that support the findings of this study was submitted as online supplemental material, and further detailed information is available upon request to the corresponding author. All genotype and phenotype resources of Korean populations are managed by “The First Korean Stroke Genetics Association Research” (The FirstKSGAR) Study constructed from the multi-centered hospital database (https://1ksgh.org/resources/data_accessibility). Futhermore, the original raw data contains potentially sensitive data including patient’s genomic profile and is access is restricted by the Ethics Committee and Institutional Review Board (IRB) of Hallym University Chuncheon Scared Hospital (https://chuncheon.hallym.or.kr/irb/index.asp). Interested researchers can submit an “The Agreement Form of Controlled Data Usage” to the Ethics Committee and IRB to request access to the data. Another WES and epidemiology data from disease-free 100 subjects (KARE study) was approved by the National Biobank of Korea, the Korea Disease Control and Prevention Agency, Republic of Korea (NBK-2022-068) (https://biobank.nih.go.kr/eng/cmm/main/mainPage.do). Access to all UKB data including sequencing and other information was acquired following project approval (application number 80385) (https://ams.ukbiobank.ac.uk/ams/resProjects).