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Paroxysmal nocturnal hemoglobinuria (PNH)

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Paroxysmal nocturnal hemoglobinuria (PNH)

Definition:

Paroxysmal nocturnal hemoglobinuria is a rare, acquired disorder of blood cells in which a specific molecule on the surface of the cells leads to premature destruction of the cells. This destruction is intermittent (paroxysmal).

Alternative Names:
PNH

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Causes, incidence, and risk factors:

PNH is caused by a defect in the formation of a protein anchor called GPI. As a result of the lack of certain surface proteins, a number of surface proteins are unable to remain tethered to the cell surface, including the proteins CD55, also called Decay Accelerating Factor (DAF), and CD59, also called Membrane Inhibitor of Complement Lysis (MIRL).

A result of the loss of these cell-surface proteins is an enhanced sensitivity to complement-mediated cell destruction. (Complement is a substance produced by the immune system.) The disease can affect people of any age.

Red blood cell, white blood cell, and platelet counts may be low. Urine may be intermittently red or brown, signifying the breakdown of red blood cells with release of hemoglobin into the circulation and then the urine.

Blood clots may form in some people. The disease may arise in relation to aplastic anemia, and may progress to acute myelogenous leukemia. Risk factors, except for prior aplastic anemia, are not known.

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