USMLE® Step 1 style questions USMLE
A 10-day-old boy is brought to the emergency department for evaluation of generalized tonic-clonic seizures. The parents note recurrent upper and lower extremity muscle spasms. He has had no fever, cough, or runny nose. The patient was born full term via an uncomplicated pregnancy and normal vaginal delivery. Family history is unremarkable. Physical examination demonstrates a neonate with rhythmic jerking movements of the upper and lower of extremities bilaterally. The anterior fontanelle is open, pupils are reactive to light, and fundi are normal. Facial examination reveals a small lower jaw, low set ears, and a submucosal cleft palate. Lungs are clear to auscultation bilaterally. Cardiac auscultation reveals a harsh holosystolic murmur at the left lower sternal border. Chest x-ray demonstrates decreased soft tissue attenuation in the right anterior mediastinum. Which of the following immunologic derrangements is most likely to be observed in this patient?