Final answer:
Paroxysmal nocturnal hemoglobinuria is associated with a defect in the GPI-anchor proteins that protect red blood cells from complement-mediated destruction, leading to hemolysis.
Step-by-step explanation:
Paroxysmal nocturnal hemoglobinuria (PNH) is associated with a defect in GPI-anchor proteins, which are components that protect red blood cells from being lysed by the complement system. The primary defect in PNH is in the PIGA gene, which is essential for the synthesis of GPI anchors. Without functional GPI anchors, proteins that protect red blood cells from complement-mediated destruction, such as CD55 and CD59, cannot attach to the cell membrane. The absence of these protective proteins renders red blood cells susceptible to complement-mediated lysis, leading to hemolysis, which is a hallmark of PNH.