What is PNH?

What is Paroxysmal Nocturnal Haemoglobinuria (PNH)?

The medical information provided on this website is by way of general guidance only. You should always contact your clinician for medical advice and do not rely upon the information provided here.

PNH is a very rare blood disease (also sometimes referred to as an ultra-orphan disease) where blood cells are vulnerable to be attacked by a particular part of the body’s immune system called “the complement”. The process by which the red blood cells are destroyed, is called haemolysis and is responsible for many of the symptoms of the disease. Haemolytic PNH affects between approximately 1 and 9 people in every one million of the population. A slightly larger proportion of the population have PNH but with few symptoms. PNH affects both men and women, all races and all ages and people can be diagnosed at any age. PNH is an acquired disease, which means it cannot be inherited and it is not contagious.

A good video explanation of PNH can be found here.

PNH can often be accompanied by aplastic anaemia (AA) but someone can have PNH without also having AA. For more information about AA, please see the Aplastic Anaemia Trust’s website.

What causes PNH?

A lot of work is being done to find out what causes PNH. If you have PNH, your bone marrow may not be working normally. Some patients develop PNH after they have had treatment for a bone marrow disorder called aplastic anaemia (AA) which causes the bone marrow to produce fewer blood cells. PNH develops when bone marrow produces a gene called PIG-A. This genetic change (mutation) happens after birth which means you acquire PNH rather than inheriting it. The PIG-A gene causes bone marrow to produce blood cells without a special protein known as the GPI anchor which protects normal blood cells against the body’s own immune system. Without the GPI anchor, PNH blood cells are not protected against a series of complex reactions called “complement activation” which is part of the body’s normal immune response to help fight infections. It is this lack of protection which allows the immune system to destroy PNH blood cells and results in haemolysis which is the main cause of the symptoms and complications related to PNH.

Not everyone who has PNH is affected by it in the same way. Some people may have no symptoms and others may have many as well as other complications.

What is a PNH “clone”?

The group of blood cells affected by the genetic defect that causes PNH is known as a PNH clone. The extent to which blood cells are affected by PNH is often described in terms of a clone size. A PNH specialist can measure the size of a PNH clone through a specialised test. Generally, if you have more than 50% of PNH blood cells, this is referred to as a large clone, 10% to 50% of PNH blood cells is a moderate size clone and less than 10% of PNH blood cells is a small clone. For more information see the PNH National Service’s website here.

Can PNH disappear?

It is possible for PNH to disappear, known as ‘spontaneous remission’ however this is not very common and it is not yet known why this happens. 

Is there a cure for PNH?

There is no cure yet for PNH, however there are successful treatments which can alleviate the symptoms. 

What does the term “Paroxysmal Nocturnal Haemoglobinuria” mean?

The name given to this disease is actually the Latin description of one of the symptoms (which not all PNH patients experience). “Paroxysmal” means intermittently, “nocturnal” means at night and “haemoglobinuria” means haemoglobin is present in the urine. Therefore, the name refers to the presence of haemoglobin (which is the pigment inside red blood cells) in urine at night. Patients will know that this pigment it is actually usually present in urine in the morning. Due to the presence of the haemoglobin in the urine, it can vary from a red to a dark brown colour.

What triggers haemolysis?

The destruction of red blood cells by the complement part of the immune system is called haemolysis. Sometimes a large number of red blood cells can suddenly be destroyed (acute haemolysis). Haemolysis tends to increase during an infection and in women, when they are having a period or during pregnancy. Some patients have increased haemolysis after air travel.

During haemolysis, you are encouraged to drink more fluids to help your kidneys flush out the excess haemoglobin and iron which is being produced. If an episode of haemolysis continues for more than 48 hours or severe abdominal pains or pain in the loin/back occurs, urgent medical advice should be sought.

What about other health problems apart from PNH?

It is important that if a PNH patient needs dental treatment or treatment for another, perhaps unrelated, medical problem (including cosmetic surgery) they should make sure they inform their medical team in case these treatments may impact or interact with their PNH.