Severe combined Immunodeficiencies (SCID) are a group of inherited diseases of the immune system by characterized profound abnormalities of B and T cell development. Infants with SCID require prompt clinical response to prevent life threatening infection and studies show significantly improved survival in babies Diagnosed at birth as a result of previous family history. SCID follows criteria for population based newborn screening since it is asymptomatic at birth and fatal within the first year of life, the confirmation of the disease is easy, there is a curative treatment, and it is known that early stem cell transplantation improves survival.To show that early diagnosis of SCID with a TREC screening assay can warrant timely treatment of the disease and avoid life-threatening infections on patients. Babies with SCID are unable to fight infections. They become severely ill in their first months of life and do not survive unless their immune systems can be restored. SCID can be treated by bone marrow transplant if recognized early. We undertake the task of newborn screening in the whole region of Shanghai, So the newborn screening test to be employed in this study is designed to diagnose SCID before infections occur. Through this study, we hope to confirm the prevalence of SCID in China and the benefits of newborn screening for early diagnosis of SCID.