Autoimmune lymphoproliferative syndromes

Autoimmune lymphoproliferative syndromes (ALPS) are autosomal dominant disorders with clinical features of various autoimmune manifestations that predominantly involve polyclonal accumulation of lymphocytes in the spleen and lymph nodes with lymphadenopathy and/or splenomegaly, and expansion of double-negative (DN) T cells in the peripheral blood. Central to the cellular pathogenesis is defective FAS-induced apoptosis, which in turn leads to dysregulation of lymphocyte homeostasis. ALPS caused by heterozygous mutations in the Fas gene (ALPS Type Ia) make up the majority of identified cases. However, other mutations, namely of the FasL gene (ALPS Type Ib) and the caspase 8 and 10 genes (ALPS Type II) are occasionally detected, whereas some patients do not present any known mutations (ALPS-III). Recently, mutations of the NRAS gene have been suggested to cause ALPS Type IV.