Some Forms of SCID Are Due to Defects in Common

question 31

Multiple Choice

Some forms of SCID are due to defects in common 'housekeeping' enzymes, such as enzymes involved in nucleotide biosynthesis pathways, that are present in all cells of the body. These genetic deficiencies cause SCID because:

• A) The enzymes responsible are normally expressed more highly in lymphocytes than in other cells of the body.
• B) The absence of these enzymes causes build-up of intermediates in the pathway that are toxic to developing lymphocytes.
• C) The absence of these enzymes deprives lymphocytes of purine nucleotides that are needed for their development.
• D) The absence of these enzymes impairs the extensive proliferation of developing lymphocytes needed to generate the large number of circulating B and T cells.
• E) The enzymes involved in these nucleotide biosynthesis pathways cannot be compensated for by redundant pathways in the cells.

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