SCID is defined by a lack of functional B and T cells which eliminates protection by humoral and cell-mediated immunity. Which of the following is true?
A. Genes coding for B and T cell receptors are mutated so the cells are incapable of binding antigens.
B. A genetic mutation renders the individual incapable of removing a toxic DNA metabolite from lymphocytes, which ultimately destroys them.
C. Genes that code for interleukin receptors are mutated so the individual's B and T cells do not receive the activation signals, rendering them useless.
D. A genetic defect disrupts the development of the lymphocytic cell lines.
E. All of the above describe cases of SCID.
Answer: E
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