A TACI Mutation in a Patient with Autoimmune Lymphoproliferative Syndrome.

Abstract

The autoimmune lymphoproliferative syndrome (ALPS) is an inherited disorder of lymphocyte apoptosis caused by defects in the Fas apoptotic pathway. It is characterized by the association of chronic lymphoid accumulation and autoimmune manifestations. In a subgroup of patients the disease progresses through antibody deficiency and its clinical and laboratory features overlap those of common variable immunodeficiency (CVID). Some CVID cases are associated with mutations in gene TNFRSF13B, encoding TACI. Aim of this study was to determine whether TNFRSF13B mutations are also associated with ALPS. Methods. Genomic DNA from 31 ALPS patients was extracted from PBMCs after informed consent. Exons and intron-exon boundaries of TNFRSF13B gene were amplified by PCR and sequenced on an ABI PRISM 310 Genetic Analyzer. Results. A T>A transition at nt 275, that determined the non-conservative substitution of Isoleucine with Asparagine (I92N), was found in exon 3 from one patient. The mutation involved the second extracellular cysteine rich domain, which is critical for BAFF binding. It was not found in 100 control chromosomes. The patient showed a classical ALPS phenotype with lymphadenopathy, massive splenomegaly that required splenectomy, hepatomegaly and immune cytopenias (neutropenia and immune thrombocytopenic purpura); he had alopecia and high ANA levels. Serum immunoglobulins were normal (IgG titers at the lower level of the range); lymphocytes showed defective Fas-induced apoptosis. Discussion. TACI mutations might contribute to the ALPS phenotype in some cases. Our data confirm the relationships between ALPS and CVID and provides a possible molecular explanation for overlapping phenotypes.