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Polycythaemia vera (PV)

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What is polycythaemia vera (PV)?

PV is a myeloproliferative neoplasm. If you have it, you will have too many red blood cells in your bone marrow (the spongy material inside some of your bones, where blood cells are made).

As a result, your blood becomes thicker than normal. Some people with PV may also have increased numbers of white blood cells and platelets.

What causes PV?

All cells in your body contain a set of instructions which tell the cell what to do and when to do it, stored inside the cells in structures called chromosomes. The chromosomes are made up of a chemical known as DNA.

The DNA is arranged in sections called genes. There are 23 pairs of chromosomes in each cell in your body. When cells divide to form new cells, normally the chromosomes stay the same in each new cell.

However with PV, something goes wrong and causes a genetic fault to occur: you may hear your doctor talk about a fault, or mutation, in the JAK2 gene. This may happen because you’ve been exposed to hazardous chemicals, but more usually because of copying a mistake when a cell was dividing. Around 95% of people with PV have this genetic fault.

The JAK2 gene is involved in the response of bone marrow stem cells to different growth factors. A growth factor is a substance which sends signals to your stem cells, so they can produce the right number of blood cells to keep you healthy.

When you have a fault with your JAK2 gene, the stem cells can start producing red blood cells even when they’ve not be ‘told’ to do so by growth factors. This results in too many red cells being produced.

It’s important to note that the genetic fault happens during a person’s lifetime. As you’re not born with it, you can’t pass it onto your children.

As well as the presence of certain genetic faults, there are other factors which might lead to a higher risk of getting PV.

Age

Your chance of getting PV increases with age. Around 95% of people diagnosed with PV are aged 40 years or older. The disease is rare in people under the age of 15 years.

Sex

PV is slightly more common in men than women; we’re not sure why.

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