 The mutation is on the long arm of the chromosome, at position 25, which is denoted as Xq25.At this position, there is a deletion in the "SH2D1A" gene, which codes for an SH2 domain on a signal transducing protein called SLAM-associated protein (SAP).The term "SH2" domain stands for src-homology 2 domain, which is a three-dimensional domain structure of about 100 amino acid residues.