Kawasaki Disease: An update on Genetics and Pathophysiology

Advances in the Etiopathogenesis and Pathophysiology of KD

Despite being initially reported almost 60 years ago, the exact etiology of KD is unknown. KD is often described as an overt immune response to an unidentified environmental or infectious trigger in susceptible children (Lee et al., 2007). This is supported by the similarities in clinical expression between KD and other infectious diseases (Rhim et al., 2019). However, unlike other infectious diseases, KD does not spread from person to person and is not responsive to antibiotics (Lee et al., 2007). The nonsimultaneous outbreaks of KD in large cities also distinguish it from other infectious diseases. Epidemiological studies in Japan and the United States suggested that a wind-borne agent may cause KD. Such an agent was proposed to possibly be carried over the Pacific Ocean, where a zonal wind pattern was found to be associated with increased KD (Rodo et al., 2011). The COVID-19 pandemic also highlighted potential triggers for KD. Children in northern Italy developed multisystem inflammatory syndrome (MIS-C), a severe inflammatory response occurring 4-6 weeks after SARS-CoV-2 exposure, sharing some features with KD, suggesting that KD might also constitute a delayed response to a viral infection (Burns, 2024). Recent studies have proposed that KD may be linked to certain strains of human microbiota, influenced by both genetic and environmental factors. The distribution and colonization of these microbiota strains vary by age and ethnicity, potentially explaining the differences in disease incidence and clinical manifestations across populations (Rhim et al., 2022). Further research is needed to fully understand the etiology and pathophysiology of KD and its relationship with other immune-mediated diseases such as MIS-C.

The higher occurrence of this condition in different ethnic groups and races suggests that genetic factors could play a strong role in the pathogenesis of KD (Luca and Yeung, 2012; Uehara and Belay, 2012). Specifically, KD’s incidence in Northeast Asian countries, including Japan, South Korea, China, and Taiwan, is massively higher (10-30 times) than in the United States and Europe (Kim, 2019). Moreover, KD incidence has plateaued in Western countries, but remains high in East Asia, with increasing trends observed in the past decades (Kim, 2019). In Japan, a higher incidence was reported in children with parental or sibling history of KD than in the general population (Takahashi et al., 2014). The lack of clarity on the disease’s pathogenesis presents a significant challenge in developing prevention strategies and underscores the need for ongoing research into potential viral, environmental, and genetic factors that may contribute to its onset (Kawasaki et al., 1974; McCrindle et al., 2017).

Ongoing research into KD’s pathophysiology (Figure 1) has provided crucial insights into its clinical manifestations, disease progression, and potential treatment strategies. KD primarily affects small and medium-sized arteries, especially the coronary arteries, and can lead to severe cardiovascular complications if left untreated. Several studies have underscored the risk of coronary artery abnormalities in a significant percentage of patients with untreated KD (Newburger et al., 2004; No et al., 2013). These abnormalities include the development of coronary artery lesions (CALs), which are the primary cause of morbidity in these patients. Classic or complete KD is defined as the presence of fever for ≥5 days and at least 4 of 5 symptoms (Table 1). In incomplete KD, only some of the symptoms of classic KD occur besides fever, with or without the presentation of CAL complications. Atypical KD is characterized by persistent fever with or without CAL presentation but with complications typically not observed in classic KD (Newburger et al., 2004).

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FIG. 1.

Factors involved in the pathophysiology of Kawasaki disease.

The exploration of the immunological landscape in KD has been pivotal in recent research, offering deeper insights into KD’s etiology and potential treatment avenues. The intensity of systemic inflammation in KD gradually increases, peaking at around the 6th febrile day, and then gradually decreases (Lee et al., 2004; Seo et al., 2018), suggesting that the host immune reaction before the peak of inflammation may be responsible for tissue cell injury, whereas that after the peak of inflammation may be responsible for tissue cell repair. The role of T cells, especially CD8 T cells, in KD, has been subject to extensive research (Hirao and Sugita, 1998; Menikou et al., 2019; Xie et al., 2022). A decrease in CD8 T cells, along with an increase in markers of early T cell activation such as CD69, has been observed (Brogan et al., 2008; Ehara et al., 2010). In addition, an altered balance between T helper (Th)17 cells and regulatory T cells during the acute phase of KD highlights the dysregulated immune response (Jia et al., 2010). Another crucial aspect of acute KD, contributing to the impaired immune regulation, is the decrease in myeloid dendritic cells possibly due to their increased recruitment to inflamed tissues or a higher rate of peripheral destruction (Tomoyuki Takahashi, 2013). Postmortem tissue studies have shown that KD develops in three sequential and linked pathological processes as follows: acute self-limited necrotizing arteritis appearing in the first 2 weeks of the disease, subacute/chronic vasculitis observed later, and finally, luminal myofibroblastic proliferation (LMP) observed months to years after disease onset (Orenstein et al., 2012). Necrotizing arteritis might result in the formation of coronary artery aneurysms (CAAs), whereas persistent subacute and chronic vasculitis and LMP can lead to stenosis and thrombosis. CALs begin to appear before the peak inflammation stage, and early control of inflammation is crucial to reduce tissue cell injury, including CALs, and patient morbidity (Lee et al., 2012). Thus, patients should receive immunomodulators such as IVIG or corticosteroids at the earliest before the peak stage (within 6 days) to reduce morbidity and prevent CAL formation.

Recent research has confirmed the important role of inflammatory markers in KD pathogenesis. Studies have highlighted the role of alarmins from the S100 protein family, such as S100A8/A9 (calprotectin) and S100A12, as well as the role of pro-inflammatory cytokines such as interleukin (IL)-1β tumor necrosis factor (TNF), in this inflammatory process (Orenstein et al., 2012). Elevated levels of Th1 cytokines, such as interferon (IFN)-γ and IL-12, and of Th2 cytokines, including IL-4 and IL-13, are a hallmark of the disease’s acute stages and are often elevated in KD (Kimura et al., 2004). These cytokines could contribute to the vasculitis and subsequent CAL formation observed in KD. Matrix metalloproteinases (MMPs) also have an important role in inflammation and tissue remodeling. The expression and activity of different MMPs, such as MMP3 and MMP9, has been demonstrated to be elevated in acute KD (Senzaki, 2006). The circulating levels of these MMPs also correlate with the development of CAAs (Matsuyama, 1999). Overall, studies focusing on the immunological aspects of KD have revealed a complex interplay of immune responses, where activated innate and adaptive immune cells infiltrate the coronary artery wall.

The discovery of different miRNAs involved in KD has also advanced our understanding of the disease’s pathophysiology and may prove beneficial in biomarker development. MiRNAs such as miR-223 and miR-145 in serum exosomes or coronary artery tissues have been associated with acute KD (Chu et al., 2017; Shimizu et al., 2013b) and offer insights into the molecular mechanisms involved in the development of cardiovascular lesions. Moreover, various studies have revealed the role of miRNA polymorphisms in KD (Xiong et al., 2022) and in the incidence of CAL. Che et al. showed that the rs1625579 T>G polymorphism of miRNA-137 increased the risk of KD in southern Chinese children (Che et al., 2018). In this study, Fu et al. demonstrated that miRNA polymorphisms may have both a positive and a negative effect on CAA development (Fu et al., 2022). Despite these intriguing findings, the molecular and cellular mechanisms underlying the different roles of miRNAs in KD warrant further exploration.

Large-scale clinical studies have been instrumental in advancing our understanding of KD, particularly in the development of predictive models. These models are crucial for the early detection and treatment of KD, which is vital in preventing severe cardiac complications. The study by Huang et al. is a prime example of how clinical data can be leveraged to enhance KD diagnosis (Huang et al., 2021). This single-center retrospective study encompassed a substantial cohort of children, allowing for a comprehensive analysis of various biological markers. The study focused on factors such as white blood cell (WBC) count and the neutrophil-to-lymphocyte ratio (NLR), both of which are markers of the body’s inflammatory response. WBC count, a commonly used indicator of infection or inflammation, is particularly elevated during the acute phase of KD, serving as a nonspecific but valuable marker (Parthasarathy et al., 2015). The NLR offers insights into the balance between the inflammatory response and the immune system’s status. This ratio becomes particularly relevant in KD due to the disease’s inflammatory nature. The study also highlighted the significance of complement 3 (C3) levels in distinguishing KD from other febrile diseases. C3 plays a pivotal role in the body’s immune and inflammatory response, making it a potentially valuable biomarker for KD diagnosis. The integration of these markers into a predictive model demonstrates a significant stride toward a more objective and reliable diagnosis of KD. Another noteworthy contribution in the understanding of KD was presented by Ning et al., which adopted a novel approach by focusing on platelet miRNAs (Ning et al., 2020). This study used small RNA sequencing to identify miRNAs that are differentially expressed in KD patients compared with febrile controls. The identification of these miRNAs is particularly groundbreaking as it opens new avenues for noninvasive diagnostic tests. Platelet miRNAs, due to their role in the pathogenesis and prognosis of KD, provide a unique insight into the disease’s molecular mechanisms (Han et al., 2017; Laurito et al., 2014). The study’s development of a prediction model based on these miRNAs showcases the potential for these biomarkers in clinical practice. The model also displayed notable sensitivity and specificity, indicating its effectiveness in distinguishing KD from other febrile illnesses. While these predictive models show great promise, their implementation in clinical practice requires further validation across diverse populations and health care settings. Importantly, the fact that some parameters are influenced by patient demographics (age) and clinical characteristics (fever duration at presentation, organ involvement, disease stage) indicates that they might represent significant confounding factors, influencing biomarker levels (WBC differential, hemoglobin, immunoglobulins, some cytokines, platelets) and need to be considered in any prediction models. Such differences may explain why scoring systems for prediction of severe cases and risk factors for CALs, including the Kobayashi score, have not proven effective across populations, even within the same nation (Seo et al., 2018). Future research should aim to refine these models, ensuring their adaptability and accessibility in various clinical environments and patient cohorts. In addition, integrating these predictive models with other diagnostic approaches, such as echocardiography and clinical symptom assessment, could lead to a more holistic and accurate diagnosis of KD.

Advances in KD diagnosis

The complex array of symptoms characterizing KD makes its diagnosis particularly challenging. The disease’s hallmark features—persistent fever, cervical lymphadenopathy, and mucocutaneous changes—overlap with those of several other pediatric conditions (Rife and Gedalia, 2020), leading to frequent misdiagnoses. This overlap is further complicated in cases of incomplete KD, where the full spectrum of classic symptoms may not be present (Sundel and Petty, 2011). Moreover, the lack of specific biomarkers or other diagnostic tests further hampers diagnosis, restricting it to rely solemnly on clinical features and resulting in uncertainties, especially in cases of incomplete KD (Sonobe et al., 2007). Thus, clinical decision-making is often delayed or results in missed diagnoses. In 2004, the American Heart Association published a list of guidelines regarding the diagnosis, treatment, and management of KD (Newburger et al., 2004). Later, in 2017, a multidisciplinary team of experts reviewed these guidelines to provide updated recommendations (McCrindle et al., 2017) (Table 2).

Accurate and prompt diagnosis of KD is crucial, considering that early treatment, particularly with IVIG, significantly reduces CALs and associated mortality risks (Kuo et al., 2012; Sundel and Petty, 2011). Furthermore, studies reveal that 15-20% of untreated patients may develop CAAs, emphasizing the need for timely diagnosis and treatment (Newburger et al., 2004; No et al., 2013). Importantly, CALs seem to develop early in KD, before the peak of inflammation, making early treatment, before the peak of inflammation, necessary to reduce the risk of CAL progression and severity (Lee et al., 2012). Research has significantly advanced our understanding of potential biomarkers, paving the way for more precise and rapid diagnostic methods in KD. Kimura et al. made a significant breakthrough with the discovery of elevated serum levels of lipopolysaccharide binding protein and leucine-rich alpha-2-glycoprotein 1 in the acute phase of KD (Kimura et al., 2017). These pivotal findings suggest that these proteins could be used for the rapid and precise detection of KD using microarray enzyme-linked immunosorbent assay (ELISA) techniques. However, the implementation of these biomarkers in clinical settings requires further validation and development of user-friendly diagnostic kits that quickly measure protein serum levels.

Another significant advancement in KD diagnostics is the identification of specific miRNAs as potential biomarkers. Jia et al. analyzed and compared the profiles of exosomal miRNAs in serum samples from KD patients against control samples (Jia et al., 2017). They identified dramatic changes (>200-fold) in specific miRNAs, such as miR-1260a and miR-4701-5p, which were found in high abundance in patients with KD but were undetectable in healthy individuals. Further validation of these miRNAs was conducted in fresh blood samples from hospitals, demonstrating that a set of four miRNAs could effectively distinguish KD from other febrile illnesses, as well as from control cases. The diagnostic capability of these miRNAs, especially their ability to differentiate KD from other febrile illnesses with similar symptoms, highlights their potential utility in clinical settings. This study also emphasized the need to use multiple miRNA pairs for accurate diagnosis, as no single pair of miRNAs could independently distinguish patients with KD from those with viral infections or from healthy individuals. These findings underscore the role of miRNAs in the pathophysiology of KD and their potential as noninvasive diagnostic tools. However, the heterogeneity in miRNA expression among patients and the need for comprehensive validation pose significant challenges in integrating miRNA detection into routine clinical practice (Kimura et al., 2017; Stenman, 2016; Jia et al., 2017).

A study conducted by Hu et al. marked a significant milestone in KD research by identifying differentially expressed proteins (DEPs) in urine samples of KD patients (Hu et al., 2019). Overall, 30 DEPs were found in the urine of patients that were not present in control cases or other febrile illnesses like pneumonia. Among them, platelet endothelial cell adhesion molecule 1 (PECAM-1) and peptidoglycan recognition protein 1 (PGLYRP1) were found to be either upregulated or downregulated in KD compared with control cases. PECAM-1, known for its role in vascular inflammation and immunity, and PGLYRP1, involved in innate immunity, have opened new avenues in understanding KD pathogenesis and may prove to be useful biomarkers in early diagnosis (reference). Further contributions to biomarker development came from the study by Li et al., who used iTRAQ gel-free proteomics to evaluate candidate diagnostic serum proteins (Li et al., 2020). This study identified six proteins in KD, including S100A8, S100A9, S100A12, peroxiredoxin-2 (PRDX2), neutrophil defensin 1 (DEFA1), and alpha-1-acid glycoprotein 1 (ORM1), that could be used as reliable diagnostic tools for KD. The study developed a high-performance KD prediction model with an impressive area under the receiver operating characteristic value of 0.94. This development facilitates the timely identification of KD, potentially enabling clinicians to initiate treatment strategies promptly.

Overall, the continued research in developing reliable biomarkers and advanced diagnostic techniques is key to improving KD diagnosis, patient outcomes, and minimizing cardiovascular complications. Although these advancements are promising, the path to a conclusive diagnostic test for KD remains in progress. The main challenges in utilizing the above-mentioned biomarkers in a clinical setting include the need for standardization of diagnostic protocols, accessibility of testing in various health care settings, and ensuring the cost-effectiveness. Future research should focus on large-scale validation protocols across diverse populations and age groups, as well as on the development of combined biomarker panels to increase the sensitivity and specificity of KD diagnostics. In addition, integrating these biomarkers into point-of-care testing devices could revolutionize the diagnosis of KD, allowing for rapid, on-site diagnosis and timely initiation of treatment, thereby preventing the progression to severe cardiac complications. Table 3 lists current and potential new laboratory biomarkers in KD.

Genetic factors in KD

Genetic studies have been integral in uncovering the susceptibility factors in KD. A genetic basis of KD is supported by the high disease prevalence in North-East Asian populations, high risk among siblings, and familial occurrence of the disease (Agarwal and Agrawal, 2017). In this regard, genome-wide association and genome-wide linkage analyses of samples from different ethnic populations have revealed the association of several susceptibility genes, including single nucleotide polymorphisms (SNPs) for the ITPKC, CASP3, FCGR2A, ORAI, CD40, IL-4 genes with the etiology and prognosis of KD and also with the development of CAAs (Burns et al., 2005; Maggioli et al., 2014; Khor et al., 2011; Onouchi et al., 2012; Thiha et al., 2019; Yamamoto-Shimojima et al., 2019) (Table 4). In addition, genes in the transforming growth factor β pathway (TGFB2, TGFBR2, and SMAD3) and B lymphocyte kinase have been identified, suggesting the involvement of these pathways in KD (Shimizu et al., 2013a; Chang et al., 2013). Several genetic polymorphisms have also been associated with IVIG resistance (Sapountzi et al., 2023).

Certain gene-gene associations have been shown to better predict the development of KD or the increased risk of CAA complications than that predicted by individual SNPs (Kim et al., 2011; Onouchi et al., 2013; Tsai et al., 2011). For instance, Kuo et al. identified the combined association of PDE2A gene (rs341058) and CYFIP2 gene (rs767007) with increased risk for KD. Furthermore, the combination of LOC100133214 gene (rs2517892) and IL2RA gene (rs3118470) significantly increased the risk of CAA (Kuo et al., 2016). Kuo et al. also reported the combined association of ITPKC gene (rs28493229) and CASP3 gene (rs113420705) with CAA formation, as well as with a higher IVIG resistance rate, relative to the effects of individual SNPs (Kuo et al., 2013).

Besides gene polymorphisms, the expression of several genes has been shown to be altered in KD. Kuo et al. examined 49 patients with KD patients relative to healthy controls or patients with other febrile illnesses and found significantly upregulated levels of HP, GRP84, and CLEC4D genes in peripheral leukocytes during the acute phase of the disease. Moreover, all three genes were significantly associated with IVIG resistance (Kuo et al., 2020). Bioinformatics analyses have been key in identifying differentially expressed genes (DEGs) in KD, which could be used as biomarkers. Using such methods, Rahmati et al. found 28 DEGs, of which MYD88, KREMEN1, TLR5, ALPK1, IRAK4, PFKFB3, HK3, CREB, CR1, SLC2A14, and FPR1 were validated by real-time polymerase chain reaction (PCR) (Rahmati et al., 2020). Cai et al. used three mRNA microarray datasets and identified 269 DEGs in KD, of which 230 were upregulated and 39 were downregulated. Further in silico analysis revealed nine hub genes, including TLR8, ITGAX, HCK, LILRB2, IL1B, FCGR2A, S100A12, SPI1, and CD8A, with statistically significantly higher expression in KD (Cai and Hu, 2022). Further studies in diverse patient populations are crucial for verifying these results and to better understand the pathophysiology of the disease, as well as to determine the predictive value of these findings in KD.

Investigating genetic predispositions in KD marks a considerable advance in comprehending the disease’s origins. These genetic insights offer potential pathways for personalized medicine and early detection strategies. However, the translation of these genetic findings into clinical practice requires careful consideration of ethical, practical, and cost-related factors. The integration of genetic data into KD diagnosis and treatment remains an area ripe for exploration and holds promise for significant advancements in patient care (Che et al., 2018; Kuo et al., 2012; Onouchi et al., 2010).

Conclusion, Limitations, and Future Perspective

KD, a major cause of pediatric heart disease, remains a complex and challenging condition in pediatric health care. Although research has advanced, the exact cause of KD is still largely unknown, making it difficult to develop specific prevention and treatment protocols. Diagnosing KD is particularly challenging due to its nonspecific symptoms often resembling other pediatric illnesses, as well as due to the absence of specific biomarkers, leading to uncertainty, especially in atypical cases. The complexity of KD’s pathogenesis requires a multifaceted approach combining clinical and immunological studies. Understanding the immunological and genetic underpinnings of KD will have crucial implications for its treatment and diagnosis. The identification of specific cytokines and immune cell alterations can guide the development of targeted therapies, potentially mitigating the disease’s cardiac complications. Although promising as diagnostic tools, serum biomarkers and microRNAs are not yet fully integrated into clinical practice due to standardization and accessibility issues. Furthermore, the results of genetic studies on KD have limited clinical implications because of the lack of definitive genetic markers in KD diagnosis, which, in any case, can be influenced by the number of subjects. Therefore, the role of biomarkers should be studied by serial examinations according to the disease stage after understanding the processes governing self-limited diseases such as KD. Future research should focus on elucidating the complete spectrum of biomarkers involved in KD, exploring their roles in disease progression, and developing comprehensive diagnostic panels.

Further advancements in understanding KD’s pathophysiology have been made possible with the GWAS studies, opening new possibilities for clarifying KD predisposition and identifying therapeutic targets. Discoveries in differentially expressed genes, gene polymorphisms, and gene-gene associations will all be valuable for the development of genetic screening tools, aiding in early detection and possibly in personalized treatment approaches. Nevertheless, turning these scientific findings into practical strategies will require continuous research and interdisciplinary collaboration. Future research should aim to translate these findings into practical, accessible, and effective clinical tools.

In conclusion, the future management of KD will require an innovative approach, as well as global collaboration. In addition, increasing the awareness about KD among health care professionals and the general public is crucial for early detection and better treatment outcomes.