Blood disorders can affect any of the three main components of blood:
Red blood cells, which carry oxygen to the body's tissues
White blood cells, which fight infections
Platelets, which help blood to clot
Blood disorders can also affect the liquid portion of blood, called plasma.
Treatments and prognosis for blood diseases vary, depending on the blood condition and its severity.
PNH affects everyone differently. Some people have only minor problems, but for others, it's much more severe. The biggest concern is blood clots, which can be deadly. About 40% of people with PNH have one at some point.
PNH comes from your genes, but you don't get it from your parents, and you can't pass it on to your kids.
A change in a gene, called a mutation, causes your body to make abnormal red blood cells. These cells lack proteins that shield them from your immune system. So your body's immune system breaks them down, a process doctors call hemolysis.
Some doctors believe PNH is related to weak bone marrow. People with a certain type of anemia, called aplastic anemia, are more likely to get PNH. The reverse is also true: People with PNH are more likely to get aplastic anemia, though not everyone does. In this condition, your bone marrow stops making new blood cells.
PNH gets its name from one of its more common symptoms. About half of people with PNH pass dark or bright red blood in their urine at night or in the morning. "Paroxysmal" means "sudden," "nocturnal" means "at night," and "hemoglobinuria" means "blood in the urine."