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A condition in which your body does not have enough haemoglobin (the oxygen-carrying component of your blood) inside the red blood cells (RBCs). Alternately, the number of RBCs may be reduced. This may cause tiredness and other symptoms and contribute to fatigue.

Proteins produced by your immune system that find and attack foreign cells, like bacteria.

Medication that stops blood from clotting. Blood clots can be a real risk for people with PNH.

Proteins that stimulate an immune response. Antigens bind to immune cells. Those cells then "present" these antigens to other parts of the immune system, which leads to one of several different types of responses. Antigens are generally considered foreign by the body and are destroyed.

Aplastic anaemia
A condition where the bone marrow does not produce enough new red blood cells and possibly all other blood cells. The term “aplastic" means that the bone marrow is unable to produce new blood cells properly. People with aplastic anaemia have lower counts of all three blood cell types: red blood cells, white blood cells, and platelets. PNH is often found in combination with aplastic anaemia.

Aspartate transaminase (AST)
An enzyme that is released by cells into blood when certain tissues or organs are damaged. AST is found in red blood cells, liver and heart cells, and muscle tissue. High blood levels of AST may be directly related to the amount of damage to particular cells.

Autoimmune disease
When your immune system does not recognize your body’s own healthy tissues and fights against its own cells.

A reddish-yellow waste product that is formed when a red blood cell dies. Too much bilirubin can be a result of the destruction of red blood cells (haemolysis) in PNH and causes yellow discoloration of skin and whites of eyes (jaundice).

Blood clot
When platelets and fibrinogen, a protein that is the essential component of the coagulation system within the blood, bind together, they form a blood clot (also called "thrombus"). These clots can block blood flow in the veins and arteries, depending on their size and location (see Thrombosis), and can cause serious problems in people with PNH.

Bone marrow
Soft tissue inside your large bones. Bone marrow contains stem cells, which form red blood cells, white blood cells, and platelets through a process called haematopoiesis.

Bone marrow aspiration
A medical test in which a small amount of liquid from your bone marrow is extracted by a needle inserted into the back of your hip. This test is often performed before a bone marrow biopsy.

Bone marrow biopsy
A medical procedure in which a small piece of solid bone, usually from the hip, is removed. May help in diagnosing PNH.

Bone marrow transplantation (BMT)
The process of replacing defective bone marrow with the body’s own (autogeneic) or someone else’s (allogeneic) bone marrow. This process can potentially eliminate all PNH cells from the bone marrow, but it involves serious risks and side effects.

Budd-Chiari syndrome
A clot within the hepatic vein, a major blood vessel in the liver. This is an unusual place for a clot and can be a sign of PNH. Anyone with Budd-Chiari syndrome should be screened for PNH.

A protein on the outside of the cell membrane that protects cells from cell death (lysis). This protein is absent from PNH blood cells because of missing anchor proteins.

When a liquid turns into a solid, such as when a blood clot is formed.

Part of your body’s defence system that destroys foreign organisms (e.g., bacteria) as well as whole cells (self or foreign). In PNH, complement is responsible for the destruction of red blood cells that lack specific protective proteins.

Complete blood count (CBC)
Test performed on a small amount of your blood that can provide information about the amount of each type of blood cell.

Creatinine is a breakdown product of creatinine phosphate in the muscle. Creatinine is excreted in the urine. By measuring creatinine, this test indicates how well your kidneys are working.

A deficiency in the number of any type of cell in your blood.

Damaging to cells.

Declaration of Helsinki
Developed by the World Medical Association (WMA), a set of ethical principles for the medical community regarding human experimentation.

Difficulty swallowing, which is a symptom that can be experienced by people with PNH.

Shortness of breath, which is a symptom that can be experienced by people with PNH.

A kind of protein that helps the body function. Almost all processes in a cell need enzymes in order for that process to occur at a reasonable rate.

Another name for a red blood cell.

Flow cytometry
A highly sensitive and accurate laboratory technique used to count and sort cells. Flow cytometry is considered the standard diagnostic test for PNH.

Free haemoglobin
Haemoglobin that has been released from red blood cells. Some suspect that the presence of free haemoglobin in the blood leads to the development of clots and damage to the organs.

A segment of a DNA molecule that contains all the information required for synthesis, including both coding and non-coding sequences. Each gene has a specific position on the chromosome map. It is genetic information that instructs how to make essential proteins. This information, which is inherited from its parent cell, determines the characteristics of a cell.

Glycosyl-phosphatidylinositol (GPI)
An important type of anchor that attaches proteins to the cell surface. PNH red blood cells lack GPI-anchored proteins. Without these GPI anchors, certain proteins are missing from the surface of cells, leaving the cells vulnerable to destruction by the body’s complement system (see Complement).

GPI-anchored proteins
Proteins that are attached to the cell surface by an anchor called GPI. In PNH, the GPI-anchored proteins are missing, which causes red blood cells to be destroyed by the immune system.

A name for any cells containing granules.

Ham test
One of the first tests developed for PNH, the Ham test looks for increased fragility of red blood cells in a mild acid. This test is no longer used as the primary diagnostic test for PNH, as flow cytometry is now considered the most accurate test for PNH.

A protein in the blood that helps to remove free haemoglobin from your body. In PNH, there is often not enough haptoglobin to “clean up" all the haemoglobin released from the destroyed red blood cells, resulting in dark urine and other consequences of PNH.

The production of blood cells, which occurs in your bone marrow. The anaemia caused by red blood cell destruction in PNH can be made worse if haematopoiesis is not sufficient. This may also occur with other diseases of the bone marrow such as aplastic anaemia (AA).

The brownish-red substance in red blood cells that carries oxygen throughout your body.

Haemoglobin in the urine. Haemoglobinuria is the technical term for the “cola-colored" or dark urine seen in approximately 25% of patients with PNH at diagnosis. When the red blood cells that are missing the protective protein are destroyed, as they are in PNH, haemoglobin is released from the red blood cells. If haemoglobin is not all processed by the body’s systems, it is sent out as waste and gives the urine a characteristic cola-brown color.

The destruction of red blood cells. Destruction of red blood cells is the main cause of major health problems associated with PNH.

The amount of your blood volume that is occupied with red blood cells.

Immune system
defence system of the organism. It exerts a protective action against intruding agents by recognizing them as foreign and subsequently eliminating them.

A condition in which the immune system is not working properly, making the body more vulnerable to infections.

Yellowing of the skin and the whites of the eyes due to too much bilirubin in the blood. Since bilirubin builds up when there is haemolysis, jaundice can occur in patients with PNH.

Lactate dehydrogenase (LDH)
An enzyme that is found in many organs in the body, and is especially abundant in red blood cells. LDH is a key marker of haemolysis, the underlying cause of the signs and symptoms associated with PNH.

A particular kind of white blood cell that regulates the body’s immune response and is extremely important in fighting infection. There are two types of lymphocytes: T cells and B cells.

The destruction of a cell. Red blood cells are lysed by complement (the body’s immune system) in patients with PNH.

Microcytic anaemia
Microcytic anaemia occurs when there is too little haemoglobin, which causes cell division within the marrow to occur for longer than normal, resulting in smaller cells.

Myelodysplastic syndromes (MDS)
A large and heterogenous group of blood disorders in which there are problems with the proper production of blood cells within the bone marrow. MDS typically occur in elderly people and have a certain risk of converting into so-called “acute leukemia." For this reason, MDS sometimes are also called “preleukemic states." PNH is sometimes, but not often, found in combination with MDS (i.e., about 2% of all PNH patients also suffer from MDS).

A deficiency of white blood cells. This deficiency is dangerous because it leaves the body with weakened defences against infection.

Most abundant type of white blood cell that attacks invading cells and is found throughout the body.

Nitric oxide
An important molecule that regulates functions such as smooth muscle tone. Depletion of nitric oxide in the bloodstream may cause dangerous clots to form, and can be associated with common PNH symptoms including abdominal pain, back pain, difficulty swallowing (dysphagia), erectile dysfunction, and pulmonary hypertension.

Packed red blood cells (RBCs)
A concentrated amount of blood in which plasma (fluid portion of blood) has been removed from the red blood cells to make transfusions easier and faster.

A reduction in the number of red and white blood cells and platelets in the blood.

An increase of symptoms or periodic attacks of a disease. PNH people may notice their urine becomes dark or have increased difficulty breathing when there is increased haemolysis (destruction of red blood cells). Their symptoms become more severe during these episodes or paroxysms.

Paroxysmal nocturnal haemoglobinuria (PNH)
A disease characterized by chronic red blood cell destruction, often resulting in serious health problems. Signs and symptoms can include stomach pain, difficulty swallowing, anaemia, shortness of breath, tiredness (fatigue), and life-threatening complications such as blood clots, kidney failure, and damage to vital organs.

The process by which white blood cells surround and kill invading cells.

The gene that forms the blueprint of the GPI anchor that attaches important proteins to the surface of cells. PNH is caused by a defect in this gene.

Platelets (thrombocytes)
Cells in your blood that are essential components in the clotting process. In concert with certain proteins, platelets help stop bleeding when you’ve cut yourself and block blood flow inside blood vessels. In certain disease states, such as PNH, they may stick together and form a potentially harmful clot inside blood vessels.

PNH clone
A group of cells in your body that are affected by the genetic defect that causes PNH. The extent to which your blood cells are affected by PNH is often described in terms of one’s clone size.

An important component of all living cells. There are many types of proteins, like enzymes and antibodies, and they are all necessary for normal function.

Red blood cells (RBCs)
Red blood cells are constantly travelling through your body delivering oxygen and removing waste (carbon dioxide). PNH red blood cells are continually attacked and destroyed by part of the body’s defence system known as complement because they are missing important protective proteins.

Young red blood cells found mostly in the bone marrow. The reticulocytes of patients with PNH are often missing protective proteins such as CD59.

The consequences of a medical condition like PNH. Stomach pain, difficulty swallowing, and erectile dysfunction can be sequelae of PNH.

The clear, yellow liquid that separates from blood after clotting has occurred. Serum can be studied to reveal much about the patient, including whether they may have PNH.

Stem cells
Cells produced in your bone marrow that can become red blood cells, white blood cells, or platelets. PNH is a disease that originates in the stem cells.

Sucrose haemolysis test
A test for PNH that involves placing red blood cells into a solution that will cut or lyse (destroy) them if they are affected by PNH. Flow cytometry is now considered the standard for diagnosing PNH.

The blocking of a blood vessel by a particle that has broken away from a blood clot at its site of formation.

The formation or development of a blood clot that often blocks blood from flowing through a vessel (vein or artery). Blood clots can cause life-threatening complications for anyone, including people with PNH. Haemolysis significantly increases the risk of blood clots in people suffering from PNH (see Blood clot).

A process performed by a healthcare professional that transfers donated blood or blood components directly into your bloodstream. It can replace some of the red blood cells you have lost from PNH and helps some symptoms temporarily.

A test performed on the urine. A urinalysis is often part of the testing used when a patient is suspected of having PNH.

White blood cells
White blood cells are the part of the immune system that destroys foreign cells in the body. These cells exist as different types: neutrophils, eosinophils, basophils, lymphocytes, and monocytes.