**3.18 Adenosine deaminase deficiency (ADA)-SCID**

ADA- SCID is a rare genetic disease caused by a mutation of a gene on chromosome 20; this gene encodes an enzyme called adenosine deaminase (ADA). The mutation can lead to lack of ADA enzyme, and the lack of ADA enzyme causes disorder of adenosine metabolism and severe combined immunodeficiency (Aiuti et al., 2002, 2009; Aiuti & Roncarolo, 2009; Bordignon et al., 1989, 1995; Ferrari et al., 1991; Gaspar et al., 2009; Mortellaro et al., 2006).
