BTK and severe combined immunodeficiency: These include X-linked agammaglobulinemia (XLA, OMIM# 300755) caused by pathogenic variants in BTK, X-linked Wiskott-Aldrich Syndrome (WAS, OMIM# 301000) due to pathogenic variants in WAS, and Severe Combined Immunodeficiency (SCID), which can be caused by over 20 different genetic defects associated with T cell deficiency (1).