This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunity disorders, Subject name: Pathology
[{'content': 'Regarding severe combined immunodeficiency disease (SCID), which of the following statements is true? \nSelect and explain. \nA. Adenosine deaminase deficiency, B. Myeloperoxidase deficiency, C. NADPH oxidase deficiency, D. C1 esterase deficiency', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Severe combined immunodeficiency (SCID) Represents a constellation of genetically distinct syndromes, all having in common defects in both humoral and cell-mediated immune responses. The most common form is X-linked (50% to 60% of cases) and hence SCID is more common in boys than in girls. The genetic defect in the X-linked form is a mutation in the common g-chain (gc) subunit of cytokine receptors. T-cell numbers are greatly reduced, and although B cells may be normal in number, antibody synthesis is impaired. The remaining cases of SCID are inherited as autosomal recessive. The most common cause of autosomal recessive SCID is a deficiency of the enzyme adenosine deaminase (ADA).There may be greater reduction in the number of T lymphocytes than of B lymphocytes.', 'role': 'assistant'}]