GWAS has identified some well-defined KD-associated loci and part of the genetic background successfully in recent studies, while it does not contribute significantly to exploring the pathogenesis of KD [24, 25]. Different from the GWAS, WES technology can explore global genetic mutations of many other complex diseases. It could discover rare mutations in the encoding sequence, which may cause its protein-coding variants that contribute to KD susceptibility. Recent studies have reported several rare protein encoding variants associated with KD by WES technology [20]. KD is a multisystem inflammatory process, presumably, the etiology is an excessive immune response to possible infection or environmental triggers in genetically susceptible individuals [26]. People with KD may be inherently prone to other diseases, especially children younger than five years. Researchers reported that the incidence of KD in Asia was higher than that in the United States and Europe [26–30], and a higher incidence of males than females [2, 31]. Studies also have reported that the incidence between brothers or sisters was higher than that of usual people [17, 30].
In this study, we performed WES to identify rare protein-coding variants responsible for KD susceptibility. And comparative analysis with evidence obtained from previously reported articles, two rare coding variants genes MYH14 and RBP3 were discovered after filtering, which showed nominal significances (ORs = 8.3945; p = 0.0346) were associated with KD. There were six amino acid mutations distributed on seven chromosome positions of MYH14 (myosin Heavy Chain 14), and one mutation on Chr10: 47351134 of RBP3 (retinoid-binding protein 3). All the allele frequencies were lower than 0.0275%, which indicated both of them were rare variants of genes.
To date, sixteen RBP3 gene variants have been recorded in the HGMD database, including eleven missense variants, three-terminal variants, one frameshift variant, and one fragment deletion variant (Fig. 2). In 2015, Arno et al first described retinal dystrophy in children caused by homozygous nonsense RBP3 mutations, highlighting the requirement for IRBP in normal eye development and visual function [32]. Yokomizo et al [33] found that elevated expression of photoreceptor-secreted RBP3 may play a role in protection against the progression of diabetic retinopathy. While in this research, rs11204213 (c.2650G > A, p.V884M) has induced amino acid changes in Val884Met, a residue in the third of four tandem homology modules [28, 34, 35]. As compared with other SNPs, it recorded larger effects on ocular axial length, the growth of the eyeball, or the development of related phenotypes such as myopia from the missense RBP3 SNPs, Therefore, previous researchers just investigated that RBP3 was thought to be associated with retinal retinoid transport and corneal changes, however, it may be referred to KD in our research. For another rare variant MYH14, sixty gene variants have been recorded in the HGMD database, within 54 missense variants, three-terminal variants, and three frameshift variants. Among these gene variants, about eight missense variants were discovered in this study (Fig. 3), however, only gene variant A1798D (chr14: rs368219210, c.5393C > A, p.A1798D) has been published before. The only research reported that homozygous MYH14 mutations may cause perineal fistulas in Anorectal malformations, based on the genetic and computer analyses, and be related to normal cloaca development by NMHC IIC localization analysis [36]. Above all, RBP3 and MYH14 both have never been reported to be associated with KD susceptibility so far, however, one main clinical manifestation of bulbar conjunctival hyperemia in KD is appeared to be related to these rare variants in our search.