Paroxysmal nocturnal hemoglobinuria and decay-accelerating factor.

The blood cells in paroxysmal nocturnal hemoglobinuria (PNH) lack several proteins, including some that regulate the activation of complement on the cell surface. Decay-accelerating factor (DAF), the first such protein to be identified, is, like all the missing proteins, affixed to the membrane by a glycolipid anchor containing phosphotidylinositol, hexoses, and ethanolamine. The defect in PNH appears to be an inability to place or maintain proteins linked in this way on the cell surface.