Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal Nocturnal Hemoglobinuria (PNH) is a rare acquired blood disorder in which a mutation in a bone marrow stem cell makes some blood cells vulnerable to the immune system protein group called complement. The resulting destruction of red blood cells is called hemolysis and releases hemoglobin into the bloodstream and urine. PNH can affect children or adults and may also cause anemia, blood clots, and problems related to bone marrow function. It is not contagious and is usually not inherited from a parent, but it requires ongoing medical care.

Symptoms vary depending on how much hemolysis is occurring, how severe any anemia is, whether the bone marrow is making enough blood cells, and whether complications such as blood clots develop. Some people have few noticeable symptoms, while others become ill quickly. Urine color is not a reliable measure of disease severity, so mild-looking urine changes do not necessarily mean mild disease.

PNH begins with an acquired mutation in the PIGA gene within a bone marrow stem cell. This creates a group, or clone, of blood cells that lack protective proteins attached to their surface by a structure called a GPI anchor. Important missing protective proteins include CD55 and CD59.

Without these protections, the complement immune system can destroy affected red blood cells inside blood vessels. This intravascular hemolysis releases hemoglobin into the bloodstream and urine, which explains the hemoglobinuria seen in some patients. The word “nocturnal” does not mean that episodes happen only at night; hemolysis can occur at any time.

PNH can occur in children or adults and is extremely rare. There are no established lifestyle, dietary, or environmental prevention targets for this disorder, so people should not blame themselves or assume that ordinary activities caused it. Hemoglobinuria causes are related to the acquired bone marrow cell mutation rather than to a person’s choices.

Thrombosis can develop in unusual veins, including veins in the abdomen or brain, as well as in more common locations, and it may be life-threatening. Ongoing hemolysis can strain the kidneys and affect other organs. The complications of hemoglobinuria depend on the extent of hemolysis, clotting, and reduced blood-cell production.

Clinicians may suspect PNH when a person has unexplained hemolytic anemia, dark urine, low blood-cell counts, thrombosis in an unusual location, or a related bone marrow disorder. Because hemoglobinuria can be intermittent or absent, testing is important even when urine appears normal.

A bone marrow examination may be used when clinicians need to assess marrow failure or another marrow disorder. Imaging and other tests may help evaluate thrombosis, kidney effects, or another possible cause of the findings. These assessments help define the extent of disease and guide treatment.

Complement-inhibitor treatment

Approved medicines that target the complement system are the main disease-directed treatment for many people with PNH. The choice of medicine, dosing schedule, and eligibility depend on hemolysis, symptoms, thrombosis risk, kidney function, and specialist assessment. Taking treatment as prescribed and attending regular monitoring visits are important because missed doses or changes in health may require medical review.

PNH can range from a small, clinically quiet clone of affected cells to severe hemolysis, thrombosis, or bone marrow failure. Its course can change over time, so symptoms and blood-test results need periodic review. Some people have PNH alongside another bone marrow disorder.

Complement-inhibitor therapy and careful monitoring have substantially improved outcomes for many patients by reducing hemolysis and clotting risk. Treatment does not remove the need for ongoing specialist care, because the PNH clone, marrow function, and treatment needs can change.

Arrange a medical evaluation for persistent dark urine, unexplained fatigue or shortness of breath, recurrent abdominal pain, unusual bruising or bleeding, or abnormal blood counts. Evaluation is especially important for someone who has a bone marrow disorder, because these findings can have several causes and may require blood testing for hemoglobinuria and hemolysis.