APDS, or Activated P13K Delta Syndrome, is a rare primary immunodeficiency that affects 1-2 people in a million. APDS occurs when there is an abnormal change in either one of two specific genes, the PIK3CD gene or the PIK3R1 gene. The genes follow an autosomal dominant mode of inheritance and are involved in making parts of a protein that help in the growth and division of white blood cells, particularly the B-cell and T-cell lymphocytes. The changes in these genes lead to the creation of an enzyme (PI3KD) that is more active than normal, causing abnormal development and control of B- and T-lymphocytes; as a result, their ability to recognize, prevent, or fight off bacterial and viral infections is reduced. Symptoms of APDS start in childhood, and patients are vulnerable to repeat infections and autoimmune/ inflammatory symptoms such as lymphoproliferation, splenomegaly, and even lymphoma. Cases of short syndrome and neurological cognitive deficit has also been observed. Patients are often misdiagnosed with other immunodeficiencies or autoimmune disorders. Diagnosis is made by a genetic test, and regular health checkups are required. Clinical trials are underway to find a treatment for APDS.