Blood cells: These develop from stem cells and are formed in the bone marrow. There are three types: red and white blood cells and platelets.
Bone marrow: The soft, spongy substance that fills the inner cavities of the bone. It’s where white blood cells, red blood cells and platelets are formed and it also contains fluid, blood vessels and fat.
Calreticulin (CALR) mutation: The calreticulin (CALR) gene was discovered in 2013 and while it is not yet fully understood, it is known that mutations in the CALR gene lead to too many platelets being produced. About 24% of people with MF and 30% of people with ET will have the CALR gene mutation.
Hemoglobin: The protein in red blood cells that carries oxygen.
JAK pathway: The Janus Kinase pathway, to give it its full name, is a chain of signals linked to the production of blood cells. If the chain goes wrong, it’s known as a dysregulated
JAK pathway and leads to MPNs.
JAK2 molecule: A molecule present in everyone’s body, which passes messages within a cell.
JAK2V617F mutation: A change in the JAK2 molecule, which triggers a dysregulated JAK pathway. The JAK2V617F mutation is found in 90-95% of people with polycythemia vera (PV), and in around 60% of those with essential thrombocythemia (ET) and 50% to 60% of people with primary myelofibrosis (MF).
MPL mutation: A change in the MPL gene that triggers stem cells to start producing platelets even when levels of platelets in the blood are not low, resulting in too many platelets. Between 5 and 10% of patients with MF and 5% of people with ET have an MPL gene mutation.
Philadelphia chromosome: A chromosomal abnormality found in people with chronic myeloid leukaemia (CML), a related condition. As PV, ET and MF are Philadelphia chromosome-negative, its absence will help your doctor diagnose the condition you have.
Stem cells: Immature cells that can develop in the bone marrow. Stem cells are able to develop into many different cell types, including blood cells. They can keep dividing, developing into mature blood cells to replenish cells in the body.
“It’s useful to remember that MPNs are chronic diseases – in most cases they remain stable for many years or may progress gradually over time. Many people with MPNs live normal lives for years without experiencing complications.”
The exact cause remains unknown but MPNs are monoclonal blood cell disorders. This means that MPNs result from a change in the DNA of a single blood stem cell, which leads to too many abnormal cells developing. This problem becomes more widespread when the original affected stem cell divides and produces clones which all have the same defect.
Doctors don’t know exactly why some people get them but there are a few factors that may raise your risk:
MPNs are considered rare diseases, which is why you may never have heard of them until you were diagnosed. In the US, a study in 2010 showed MF affected just 3.6 to 5.7 people for every 100,000 population while there were 45-57 cases of PV per 100,000 and 39-57 cases of ET per 100,000.The accepted Canadian definition of a rare disease is one that affects fewer than 50 people out of 100,000, so it’s not surprising most people haven’t heard of MPNs.
Cancer occurs when normal cells grow in an uncontrolled way, and there has been some debate in medical circles about whether or not MPNs are types of cancer.The Canadian Cancer Society refers to them as “disorders” among the different types of blood cancers (leukemia)while the Leukemia and Lymphoma Society of Canada calls them “blood cancers.”
This depends on the type of MPN you have and its severity, as well as your age and overall health. If your symptoms are not affecting your day-to-day quality of life, your doctor may suggest they monitor the progression of your condition with regular check-ups. This approach is known as “watch and wait.” If you feel unwell, speak with your doctor.
MPNs can’t be cured, with the potential exception of MF in a small minority of people who have a bone marrow or stem cell transplant. Patients are individually assessed as transplants are not commonly recommended. This is due to a high risk of life-threatening side effects, as well as a risk that the new stem cells will react against your body’s healthy tissues. Transplants are often only considered an option for fit patients with advanced disease. The first step involves very high levels of chemotherapy or radiation therapy.
For information about managing MPNs, click here
MPNs largely affect men and women over 60,or whom pregnancy isn’t on the agenda, but they can sometimes develop in people of childbearing age, too. As MPNs are rare, very little research has been done in this area so there are no specific guidelines for doctors. While pregnancy isn’t thought to affect MPNs, how your symptoms are managed may have an effect. Plus, there are extra considerations for pregnant women with MPNs, as pregnancy may further increase the risk of having a blood clot.If you’re thinking about trying to conceive, always speak to your doctor about whether now is the best time. And if you do become pregnant, be aware that you’ll need specialist care.