Background: Little is known regarding the epidemiology of idiopathic nephrotic syndrome (INS) in East Asia. Previous studies have suggested higher incidence of INS in Asian children, though decreasing trend of its incidence has also been shown.
Methods: We conducted a nationwide study of Japanese children aged 6 months to 15 years with INS. Children who were newly diagnosed with INS between 1 January 2010 and 31 December 2012 were eligible. Children with congenital nephrotic syndrome or nephrotic syndrome secondary to nephritis were excluded.
Results: A total of 2099 children were initially diagnosed with INS and were followed for up to 4 years. The estimated incidence of INS was 6.49 cases/100,000 children per year, without clear correlation with geographical region. The male:female ratio was 1.9 and approximately 50 % of children were <5 years old at diagnosis. During the 1-4 years follow-up, 32.7 % developed frequently relapsing nephrotic syndrome and steroid-dependent nephrotic syndrome.
Conclusions: Based on our nationwide survey, the incidence of INS in Japanese children is approximately 3-4 times higher than that in Caucasians. However, the male:female ratio and the age at onset were similar to those in previous studies. We are now planning a prospective cohort study to examine the course of INS in Japan.
Keywords: Asia; Children; Epidemiological study; Idiopathic nephrotic syndrome; Incidence; Nationwide survey.