Q. A 6-year-old male child is brought to the outpatient clinic because of abnormal gait. The patient's medical history is significant for a recent upper respiratory infection that has responded well to conservative management. His mother says, "He catches the flu very easily. He got 4 attacks in the last 6 months". Upon examination, the patient has an ataxic gait with right-sided dysmetria on finger-to-nose test and ataxia with heel-knee-shin testing. Slit lamp examination reveals multiple dilated conjunctival capillaries. Which of the following genetic mutation is expected in this patient?