Myeloproliferative neoplasms (MPNs) develop when certain blood cells undergo gene changes (mutations). These changes cause the cell to begin growing abnormally.
Gene mutations increasingly collect in cells over time, and they become more numerous as a person gets older. Therefore, older adults are more likely to have gene mutations that lead to MPNs than are children or younger adults.
Researchers use a term called “median age at diagnosis” to convey when people are generally diagnosed with a condition. The number tells you that half of people with the condition are the median age or older when they are diagnosed.
The median age at diagnosis for different types of MPNs are as follows:
MPNs can affect younger people, but this is not as common. About 12 percent of people with MPNs are under the age of 40.
Certain types of MPNs may be more likely to occur in children or younger adults. For example, about 2 out of 10 people with ET are younger than 41 years old when they are diagnosed, while only 1 out of 10 people with PV are under 40.
In order to understand the link between MPNs and aging, it helps to know how MPNs begin. These conditions develop from cells called hematopoietic stem cells (HSCs).
HSCs typically live in the spongy bone marrow tissue found within certain bones. HSCs are responsible for making all of the different types of blood cells — red blood cells, white blood cells, and platelets.
Like other cells in the body, HSCs carry many different genes. Genes act as instructions that tell each cell when to divide and produce new cells, when to stop growing, and how to carry out different tasks.
Genes occasionally undergo changes. Sometimes, the resulting mutations have no effect on the way a cell operates. Other times, they may cause a cell to behave abnormally.
Gene mutations may cause a cell to grow too quickly or ignore signals telling it to stop dividing. They also can render a cell unable to repair damage. This can make a normal cell change, leading to MPNs or other blood conditions.
When certain genes become mutated within HSCs, the HSCs stop working properly. They start making too many blood cells, which can go on to cause several problems within the body.
Almost all people with chronic myeloid leukemia have a gene change called the Philadelphia chromosome, in which two different genes become improperly fused together. This leads to a new gene, BCR-ABL1, that encourages cells to grow.
MPN cells also frequently contain additional mutations in genes such as:
These mutations may play a role in which MPN symptoms a person experiences or their disease outlook.
Gene mutations build up over time. Although an MPN-causing mutation could occur at any point in a person’s life, the chances of this happening rise the more a person ages.
In general, several factors can cause gene mutations. Genes can be damaged when a cell is exposed to things like radiation, ultraviolet light, cigarette smoke, or certain chemicals. Additionally, gene mutations can develop during the process of cell division (when a parent cell divides in order to form two new cells).
During cell division, the parent cell copies its DNA (the substance that contains genes). It then passes on one copy to each of the two new cells. Occasionally, the cell makes a mistake when it is copying a particular gene, leading to a mutation.
Many types of cells don’t typically grow and divide frequently after a person goes through development. However, the body is constantly making new blood cells. HSCs and other immature blood cells go through cell division frequently in order to produce new, mature blood cells.
This means that new mutations are constantly forming and being passed on to other cells. Researchers estimate that by the time a person turns 60, these quickly dividing cells could contain tens of thousands of mutations.
These mutations within blood cells can lead to a condition called clonal hematopoiesis (CH). CH is very common in older adults. It doesn’t cause symptoms, so most people don’t know they have it.
CH occurs when an HSC develops mutations and then goes on to create many copies of itself. This causes a person to have large numbers of blood cells that contain potential MPN-causing gene changes, including JAK2, DNMT3A, and TET2 mutations.
CH is not cancer. However, it leads to an increased risk that a person will develop blood cancers, including MPNs. When a person has CH, it is an indication that they likely have HSCs that contain high-risk gene mutations.
All in all, the older a person gets, the more mutations their blood cells will accumulate. The more mutations a cell contains, the higher the chances that it will turn cancerous.
On myMPNTeam, the social network for people living with myeloproliferative neoplasms and their loved ones, more than 1,800 members come together to ask questions, give advice, and share their stories with others who understand life with MPNs.
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