This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Primary Immunodeficiency, Subject name: Pediatrics
True about SCID in children is: 
Select and explain. 
A. It is due to adenosine deaminase deficiency, B. Humoral immunity is predominantly affected, C. Child should receive double dose of all vaccines, D. Patients with SCID have normal thymus
A: It is due to adenosine deaminase deficiency
Answer: A: It is due to adenosine deaminase deficiency 
Explanation: SCID: It is due to adenosine deaminase deficiency SCID- combined antibody and cellular defect Live vaccines are contraindicated in SCID Patients with SCID have very small thymus; tonsils & adenoids are also absent or underdeveloped