Primary immunodeficiencies (PIDs) are inherited disorders in which one of morecomponents of the immune system are missing or do not work properly. PID patientsare more susceptible to certain type of infections and have increased risk ofautoimmune diseases and malignancies. The majority of PIDs are autosomalrecessive inherited disorders and they are commonly considered as rare disease inWestern countries, however high rate of consanguinity has resulted in a highprevalence of PID in Turkey. Unfortunately, the lack of facilities to perform geneticanalysis for PIDs remains a significant problem in Turkey. Since 2011, ourdepartment has established genetic analysis for candidate genes involvedagammaglobulinemia, CVID and SCID. Moreover, in recent years, next generationsequencing has represented as a promising molecular diagnostic tool for inheriteddiseases, especially for discovery of potential new candidate genes in PIDs. Incollaboration with the department of Advanced Genomics and BioinformaticsResearch Center at TUBITAK and department of Pediatrics and Adolescent ofUniversity of Hong Kong, a preliminary study has been started. Eightagammaglobulinemia patients without BTK mutation, were further analyzed usingnext generation sequencing (NGS) and mutations were found in IGLL1, NHEJ1,CHD7, WASP, CD19 and RAG1 in these patients. Currently we are confirming theresult of the NGS data with conventional Sanger sequencing. Our resultsdemonstrate that NGS is an effective method for diagnosis of PIDs.For development of alternative treatment for PID, we investigate whether stem cellbasedgene therapy using the lentiviral vectors could provide a novel treatmentoption, in particular for X-linked agammaglobulinemia (XLA). X-linkedagammaglobulinemia (XLA) is the most common primary immunodeficiency diseasein man. The disease is caused by mutations in the Bruton's tyrosine kinase (BTK)gene and characterized by an arrest of B cell development in bone marrow andabsence of immunoglobulins. Patients often develop recurrent and severe bacterialinfections caused by pyogenic bacteria such as pneumococci and streptococci.Although current IVIG treatment for XLA is fairly effective and the quality of life ofmost patients has significantly improved, recurrent infections cause progressive andirreversible organ damage, particularly of the lung and consequently represent a lifethreateningrisk. We transplanted Btk-/- mice sublethally irradiated with lineagemarker-depleted bone marrow wild-type cells, Btk-/- cells untransduced ortransduced with the self-inactivating lentiviral vector and analyzed B-cellreconstitution in bone marrow, spleen, and peritoneum. Btk-/- mice engrafted withtransduced cells showed correction of B-cell in bone marrow, spleen and blood. Alltreated mice exhibited the recovery serum immunoglobulins as well as responses toT cell-independent antigens. Moreover, transplantation into secondary Btk-/-recipients resulted in functional restoration of B cells and serum immunoglobulins,without any adverse effects.