A test for the exclusion or confirmation of PNH should be considered in patients
with otherwise unexplained thrombembolic complications, or in patients with hemolysis
or hemorrhage, anemia, and other symptoms.
Patients with PNH have a defective gene called PIG-A,
involved in the biosynthesis of glycosyl-phosphatidylinositol (GPI). Without
GPI, important regulatory proteins
(e.g. CD55 or “DAF”, and CD59 or “MIRL”) cannot bind
to the cell surface and protect blood cells from attacks of complement. This
may result in a break down of erythrocytes and release of hemoglobin which
causes the urine to turn dark during an episode (or “paroxysm”)
of hemolysis, though this is not found in all cases.
PNH is an acquired condition induced by exposure to chemicals or certain antibiotics.
In many patients their PNH cells may disappear from the blood after some time.
Repeating a test for PNH may help to identify patients who are likely to have
a spontaneous cure.
Treatment of PNH includes immune-suppressive
drugs, supplementation with iron and folic acid. Blood transfusions or anticoagulation
may be needed.
Alexion Pharmaceuticals, Inc., a humanized antibody against complement C5)
is a new drug used to treat PNH*. Eculizumab treatment reduces the risk of
clinical thromboembolism in patients with PNH**.
*Rother RP, et al. Discovery and development of the complement inhibitor eculizumab
for the treatment of paroxysmal nocturnal hemoglobinuria. Nat Biotechnol. 2007;25:1256-64.
**Hillmen P, et al.. Effect of the complement inhibitor eculizumab
on thromboembolism in patients with paroxysmal nocturnal hemoglobinuria.Blood.