Representations of SH2D1A/SAP and BIRC4/XIAP. (A) SH2D1A (SH2 domain protein 1A) has 4 exons and codes for a small protein, SAP, with only 128 amino acids that form 1 SH2 domain (amino acids 6-104). Previously unreported mutations observed in patients with XLP1 tested through the DCHI at Cincinnati Children's Hospital are shown. (B) BIRC4 (baculoviral IAP repeat-containing protein 4) is composed of 6 exons and codes for XIAP, which is 497 amino acids long. XIAP contains 3 BIR domains and 1 RING domain. Mutations observed in patients with XLP2 tested through the DCHI at Cincinnati Children's Hospital and by Rigaud et al²  (*) and Zhao et al⁵⁰  (**) are shown.