Primary immunodeficiency (PID) constitutes a large group of diseases, including almost 180 hereditary disorders. The patients show susceptibility to various infections due to congenital defects of the immune system. It is also known that PID patients suffer from non-infectious complications, including autoimmune diseases and malignant disorders. During the last 20 years the number of known PID has increased considerably. New PID conferring a specific predisposition to infections with one or a few pathogens have been described. Disorders of innate immunity and various autoinflammatory disorders were included in new categories. In contrast, the incidence, clinical manifestations, and genetic factors of PID seem to be different among countries or races. The clinical manifestations can differ depending on the hygiene conditions, health-care environment, and vaccination policy, and so on. A nationwide survey on PID patients in Japan provided a lot of information regarding these issues, and it uncovered a previously unknown complication of PID, endocrine disorders. In this review, the data concerning epidemiology and clinical characteristics of PID in Japan obtained in the nationwide questionnaire survey, and the results of studies on the clinical and genetic characteristics of Japanese patients with Mendelian susceptibility to mycobacterial disease and interleukin-1 receptor-associated kinase 4 deficiency are presented in the light of their pathogenesis and pathophysiology.
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