SASH3, also called SH3-containing lymphocyte protein (SLY1), is a putative adaptor protein. It is postulated to play a crucial role in organizing signaling complexes and propagating signal transduction cascades in lymphocytes. It is involved in pathways like natural killer cell-mediated cytotoxicity, Th17 cell differentiation, and multiple immune-related signaling pathways [1,3].

In humans, deleterious variants in SASH3 cause a novel form of X-linked combined immunodeficiency with immune dysregulation. Patients show recurrent infections, autoimmune cytopenias, and lymphopenia of multiple cell types, along with impaired T-cell functions such as proliferation and survival [1]. In a case, an adult patient with a SASH3 loss-of-function variant initially diagnosed with common variable immunodeficiency had abnormal immunological phenotypes [2]. Also, a patient with an SASH3 germline mutation had autoimmune haemolytic anaemia and immune thrombocytopenia, showing the role of SASH3 in immune-mediated cytopenias [4].

In conclusion, SASH3 is essential for lymphocyte function and survival. The study of SASH3-deficient models, both in humans with genetic mutations and potentially in mouse models (by inference from the identified human phenotypes similar to mouse Sly1-related phenotypes), has revealed its significance in immunodeficiency and immune dysregulation diseases, highlighting its potential as a key factor in understanding and treating such conditions [1].