Combined immunodeficiency due to STK4 deficiency is a rare, inherited disorder that affects the immune system. It is caused by mutations in the STK4 gene, which is responsible for producing a protein called serine/threonine kinase 4. This protein is important for the development and function of certain immune cells, such as T cells and B cells. People with this disorder have a weakened immune system, which makes them more susceptible to infections. Treatment typically involves antibiotics, immunoglobulin therapy, and bone marrow transplantation.