Gene therapy for severe combined immunodeficiency.

Studies of severe combined immunodeficiency (SCID), a group of rare monogenic disorders, have provided key findings about the physiology of immune system development. The common characteristic of these diseases is the occurrence of a block in T cell differentiation, always associated with a direct or indirect impairment of B cell immunity. The resulting combined immunodeficiency is responsible for the clinical severity of SCID, which, without treatment, leads to death within the first year of life. Eleven distinct SCID phenotypes have been identified to date. Mutations of ten genes have been found to cause SCID. Identifying the pathophysiological basis of most SCID conditions has led to the possibility of molecular therapy as an alternative to allogeneic hematopoietic stem cell transplantation. This review discusses recent developments in SCID identification and treatment.