[Major histocompatibility complex class II deficiency].

Major histocompatibility complex class II deficiency is an autosomal recessive primary combined immunodeficiency. The prevalence of this deficiency is highest in Mediterranean areas, especially north Africa. Early diagnosis is essential due to high mortality in the first 2 years of life and the possibility of bone marrow transplantation. We report four cases of major histocompatibility complex class II deficiency and describe their epidemiologic and clinical characteristics, diagnostic tests, treatment and outcome.