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Multisystem Inflammatory Syndrome in Children (MIS-C) is a rare febrile disorder with multisystem organ involvement temporally associated with coronavirus 2019 infection (COVID-19) and frequently exhibits features mimicking Kawasaki disease (KD), another febrile disorder in children. The pathogenesis and the full clinical spectrum of MIS-C is poorly understood: It is still unclear whether MIS-C and KD are different syndromes or represent a common spectrum. The erythema and induration of Bacillus Calmette-Guérin (BCG) scar is one of the characteristic findings of KD, and is useful for the diagnosis in countries where BCG vaccination is mandated in infancy. Furthermore, such findings in BCG scar were also reported after SARS-CoV-2 vaccination, which may be related to molecular mimicry. However, there are no reports of changes at the BCG scar in MIS-C cases. Here, we report a case of MIS-C in a 3-year-old Hispanic boy in Japan, with erythema and induration at the BCG scar. The patient received BCG vaccination at 16 months of age in Japan. Four weeks before the onset, he had positive polymerase chain reaction (PCR) results for SARS-CoV-2 following household outbreak, although he was asymptomatic. He presented with fever and gastrointestinal symptoms, followed by the appearance of all six principal findings of complete KD. He exhibited congestive heart failure, following intravenous immunoglobulin (IVIG) therapy. He was diagnosed with MIS-C based on characteristic mucocutaneous and gastrointestinal symptoms, decreased cardiac function, and coagulopathy, in addition to laboratory data consistent with MIS-C. The BCG finding was present from the early stage of the disease. The patient was refractory to two doses of IVIGs, and the third IVIG plus prednisolone resulted in defervescence and improvement in heart failure. No coronary involvement was observed. This is the first case of erythema and induration at the BCG scar associated with MIS-C accompanied by KD features, which may give clinical and mechanistic insights in the understanding of the disease. Since the full spectrum of MIS-C is still evolving and both of them are syndromes with overlapped clinical features, further studies are warranted for deep phenotyping of MIS-C with KD features relative to KD in countries with mandatory BCG programs in infancy.

Background Patients with pulmonary arterial hypertension (PAH) carrying bone morphogenetic protein receptor type 2 (Bmpr2) mutations present earlier with severe hemodynamic compromise and have poorer survival outcomes than those without mutation. The mechanism underlying the worsening clinical phenotype of PAH with Bmpr2 mutations has been largely unaddressed in rat models of pulmonary hypertension (PH) because of the difficulty in reproducing progressive PH in mice and genetic modification in rats. We tested whether a clinically-relevant Bmpr2 mutation affects the progressive features of monocrotaline (MCT) induced-PH in rats. Methods A monoallelic single nucleotide insertion in exon 1 of Bmpr2 (+/44insG) was generated in rats using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9, then PH, pulmonary vascular disease (PVD) and survival after MCT injection with or without a phosphodiesterase type 5 inhibitor, tadalafil, administration were assessed. Results The +/44insG rats had reduced BMPR2 signalling in the lungs compared with wild-type. PH and PVD assessed at 3-weeks after MCT injection were similar in wild-type and +/44insG rats. However, survival at 4-weeks after MCT injection was significantly reduced in +/44insG rats. Among the rats surviving at 4-weeks after MCT administration, +/44insG rats had increased weight ratio of right ventricle to left ventricle plus septum (RV/[LV + S]) and % medial wall thickness (MWT) in pulmonary arteries (PAs). Immunohistochemical analysis showed increased vessels with Ki67-positive cells in the lungs, decreased mature and increased immature smooth muscle cell phenotype markers in the PAs in +/44insG rats compared with wild-type at 3-weeks after MCT injection. Contraction of PA in response to prostaglandin-F2α and endothelin-1 were significantly reduced in the +/44insG rats. The +/44insG rats that had received tadalafil had a worse survival with a significant increase in RV/(LV + S), %MWT in distal PAs and RV myocardial fibrosis compared with wild-type. Conclusions The present study demonstrates that the Bmpr2 mutation promotes dedifferentiation of PA smooth muscle cells, late PVD and RV myocardial fibrosis and adversely impacts both the natural and post-treatment courses of MCT-PH in rats with significant effects only in the late stages and warrants preclinical studies using this new genetic model to optimize treatment outcomes of heritable PAH.

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