Q. A 3-month-old girl has been referred to the hospital for persistent diarrhea, jaundice, and recurrent lung infections. Her birth history shows she is born out of consanguineous marriage at full term with low birth weight. Her family history shows that her elder sister died of recurrent infections at the age of 8 months. Her temperature is 102°F (38.8°C), pulse 70/min, blood pressure of 50/34 mm Hg, and respiratory rate of 46/min. Physical examination shows a severely sick child with head and body circumferences at less than the 3rd percentile. She has a diffuse macular rash over her body and has oral thrush. Lymph nodes are absent on palpation. Bilateral basal rales heard on auscultation. Lab investigations are shown below. Mutations in which of the following genes is most likely responsible for her condition?