Features of pediatric idiopathic nephrotic syndrome in the Sakishima Islands, Japan: An epidemiological study

Objective: This epidemiologic study aimed to elucidate the incidence and clinical characteristics, including the different responses to prednisone and relapse status, of pediatric idiopathic nephrotic syndrome (INS) in the genetically diverse population of the Sakishima Islands, which is located southwest of the main island of Okinawa, Japan. Methods: This longitudinal cohort study included children diagnosed as INS at the age of ＜16 years and who were treated at the two existing pediatric inpatient facilities in the Sakishima Islands. Data from the electronic medical records from 2005 (Miyako Hospital) or 2012 (Yaeyama Hospital) to April 2023 were analyzed. The initial treatment followed the International Study of Kidney Disease in Children regimen, and outcomes were defined according to international guidelines. Results: Among 25 new cases of INS (17 boys), the median age of onset was 3 years. Notably, the incidence of INS started to increase in 2010, ranging from 6.93-12.64 per 100,000 children, and peaked between 2015 and 2019. Majority of the cases were steroid-sensitive nephrotic syndrome (SSNS), and the transition to frequently relapsing nephrotic syndrome (FRNS) was faster in the Miyako Islands than in the Yaeyama Islands. Conclusions: Compared with mainland Japan, the Sakishima Islands had a higher incidence of INS, with distinct regional clinical patterns. These findings suggested that genetic and environmental factors contributed to the epidemiology of INS and supported the dual structure model of genetic influence in Japan. Future research, including genetic analysis, may further clarify these regional differences and improve treatment strategies.