One form of anemia results when individuals have a deficiency in the enzyme phos

Question

One form of anemia results when individuals have a deficiency in the enzyme phosphatidylinositol glycan A (PIGA). This enzyme is required the membrane attachment of proteins anchored by glycolipids to the plasma membrane, using what is called a GPI-linkage. Included in the group of GPI-linked cell surface proteins is DAFICD55. These individuals become anemic because: O A DAFICD55 normally prevents the spleen from clearing healthy red blood cells from the circulation O B.DAF/CD55 prevents the lysis of red blood cells by infecting pathogens. OC. DAFICD55 is a complement inhibitory protein that inactivates any C3 convertase that may form on host cell surfaces O D. In the absence of PIGA, red blood cells are unable to synthesize high levels of hemoglobin. OE. In the absence of PIGA, the red blood cell membrane is bare of proteins allowing increased access of complement activating proteins to attach to the cell membrane.

Explanation / Answer

Answer: E.) In the absence of PIGA, the red blood cell membrane is bare of proteins allowing increased access of complement activating proteins to attach to the cell membrane.

Explanation: If the PIG-A gene is mutated then the GPI anchor synthesis does not happen. As mentioned in the question, DAF/CD55 is a kind of GPI linked cell surface protein. The  DAF/CD55  limits the amplification of convertases of the complement cascade and indirectly blocks the formation of the membrane attack complex. Thus in people with a mutation in the PIGA protein, the RBCs get lysed due to such complement mediated membrane attack complexes, thereby leading to anemia.

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