Abstract: ObjectiveTo explore the clinical features of Kawasaki disease (KD) complicated with macrophage activation syndrome (MAS) and the biological significance of related gene and protein expression.MethodsClinical data and laboratory results of patients with MAS in KD admitted to Children's Hospital of Chongqing Medical University from August 2008 to June 2017 were retrospectively studied and compared with the patients from published literature. The patients were divided into two groups according to the prognosis: improvement group and poor prognosis group (dead or abandoned therapy).ResultsThe incidences of clinical manifeststions in 9 children with KD complicated with MAS in our study were as follows: hepatosplenomegaly and intravenous immunoglobulin (IVIG) unresponsiveness 100%(9/9), rashes 88.9%(8/9), changes in the extremities 88.9%(8/9), changes in the lips and oral cavity 77.8%(7/9), lymphadenopathy 66.7%(6/9), bilateral conjunctival injection 44.4%(4/9), coronary lesions 88.9%(8/9), incomplete KD 44.4%(4/9). C-reactive protein (CRP) increase, fibrinogen ＜ 1.5 g·L-1 and ferritin level >1 500 ng·mL-1 were found in 8 patients separately. The rates of alanine aminotransferase (ALT) increase, aspartate aminotransferase (AST) increase, hemophagocytic phenomenon in bone marrow and triglyceride (TG)＞3.0 mmol·L-1 were 77.8%(7/9), 66.7%(6/9) , 66.7%(6/9) and 44.4%(4/9), respectively. HLH-related gene and protein expression were measured in 2 children with MAS in KD. Reduced expression of perforin in NK cells was detected in 2 cases, but reduced granzyme B in NK cell and reduced perforin in CTL cells were found in only one case. No mutation of 24 genes related to HLH was found in 2 cases. A total of 27 patients with MAS in KD (including 9 cases in our study) were enrolled based on the literature review. According to the prognosis, 27 cases were divided into improvement group (18 cases) and poor prognosis group (9 cases). The incidence of incomplete KD in poor prognosis group was higher than that in the improvement group (55.6% vs 5.9%, P=0.004). ConclusionMAS complicating with KD should be considered when KD children are with IVIG unresponsiveness, hepatosplenomegaly, elevated AST and ALT, hyperferroteinemia. KD complicated with MAS showed no genetic susceptibility. Reduced perforin expression may be closely related to KD-MAS. Incomplete KD may be one of the risk factors affecting the prognosis of children with KD-MAS.