PSTPIP1 is a 416 amino acid protein that localizes to both the cytoplasm and the cytoskeleton and contains one SH3 domain and one FCH domain. Expressed at high levels in T cells and spleen and present at lower levels in thymus, lung, placenta and small intestine, PSTPIP1 interacts with CD2AP, BDP1 and c-Abl and is involved in the regulation of the Actin cytoskeleton, possibly functioning as a scaffold protein that may promote Actin polymerization. Defects in the gene encoding PSTPIP1 are the cause of PAPA syndrome (PAPAS), an autosomal dominant disease characterized by recurring inflammatory episodes that affect skin and joint tissue. Multiple isoforms of PSTPIP1 exist due to alternative splicing events.