Q. A 3-month-old male child is brought to the emergency department because of abnormal behavior. His mother mentions that he has appeared "out of it" since yesterday and frequently rubs his right ear. The patient's medical history is significant for X-linked thrombocytopenia diagnosed shortly after birth and also two attacks of pneumonia. Upon examination, the right tympanic membrane appears red and erythematous with mild suppuration. The patient is diagnosed with acute otitis media. Which of the following genetic defects is suspected in the above patient?