Is fibromyalgia hereditary?

You can find the video after the text

A while ago I was asked if fibromyalgia is hereditary. I have met many with fibromyalgia and know that it is common that close relatives of those affected also have the diagnosis. But to get more knowledge about how it is, I looked at the research and I think I received clear answers, which this film will be about.

My name is Andreas Persson and I am a physiotherapist and specialist in pain and pain rehabilitation. What I say in the film can be found in text form together with references to the scientific literature it is based on. The link is in the description.

To be able to determine if fibromyalgia is hereditary, we need to look at what is meant by heredity and how to measure it.

The fact that a disease is hereditary means that it is caused by genes. The characteristics and diseases that we get are determined by the genes we get from our parents or the environment or a combination of the genes and the environment. The environment is everything you have been exposed to since you were born and also before you were born through the environment you were exposed to when you lay in your mother’s womb.

Some diseases are completely genetic, that is, they are determined only by genes. An example is Cystic fibrosis which is caused by a change in a gene that regulates the transport of salt through the cells in the body, which in turn, among other things, impairs the function of the lungs and gastrointestinal tract. To get the disease, you must have received the altered gene from both your mother and your father. Everyone who gets the altered gene from both their parents develops the disease.(1) Some would say that such a disease is hereditary while other diseases that are not just due to genes are not.

Most diseases, however, depend on both genes and environment, that is on the genes you received from your parents and the environment you were exposed to since dad’s sperm fertilized mom’s egg. In this context, one does not talk about whether the disease is hereditary or not hereditary, but about how large the heredity or more correct the heritability is, that is how much of the risk of developing the disease is determined by the genes and how much is determined by the environment one has been exposed to.

There is a very good way to calculate how much heritability a disease has. Because identical twins share 100% of the same genes and fraternal twins share only 50% of the genes, twin studies comparing identical and fraternal twins can be designed to figure out how much of the risk for a disease is inherited.(2)

If you find out who has a certain disease among the twins, you can see how common it is that the other twin sibling also has the same disease. If it is just as common for the other twin sibling to have the disease among fraternal twins that share 50% of the genes as in identical twins that share 100% of the genes, then heritability is 0%. This means that the disease is caused 100% by the environment. Had heritability been more than 0%, it would have been more likely to have the same disease if you have 100% of the same genes than if you only have 50% of the genes in common.(2)

If 50% of the twin siblings of fraternal twins have the same disease and 100% of the twin siblings of identical twins have the same disease, then the heritability of the disease is 100%.(2)

Siblings who are not twins, but where both parents are common share just like fraternal twins 50% of the genes with each other because both have received their genes from the same parents, albeit randomly different genes from different parents. It is also the case that a parent shares 50% of the genes with their child because the child received half of the genes from the parent and the other half from the other parent.(2) When I talk about close relatives in the video, I mean siblings, parents or children, that is, those who share 50% of the genes with the person being compared.

But let’s get to the point. How big is the heritability for fibromyalgia? Twin studies have shown that the heritability of fibromyalgia is about 50%, which means that 50% of the risk of developing the disease is determined by which genes you have and 50% is determined by the environment you are exposed to.(3)

But what does heritability of 50% mean in practice? The average incidence of fibromyalgia is approximately 2.7%.(4) Park and co-workers presented in a compilation of studies how common fibromyalgia is in close relatives of people with fibromyalgia. One study looked at 20 families where the mother in the family had fibromyalgia. Of the 58 children in the families, 16 had fibromyalgia, that is, 28%.(5)

In another study of close relatives of thirty women with fibromyalgia, 26% of the close relatives met the criteria for the disease. Among male close relatives, 14% had fibromyalgia and among women, 41% met the diagnostic criteria.(6) This is not surprising given that fibromyalgia is significantly more common in women than men, but it shows that the risk of the disease is greater in women who have a close relative with fibromyalgia than in men who have it.

These studies show that if you have a parent, a sibling, or a child who has fibromyalgia, the risk of having it yourself is about ten times higher than for anyone. Based on the studies, it can be concluded that if a mother has fibromyalgia, the risk that the child will develop fibromyalgia is about 25%. If one sibling has the disease, the risk that a specific other sibling also has fibromyalgia is 25%.

A third study compared the proportion of close relatives of people with fibromyalgia who had fibromyalgia with the proportion of close relatives of those with rheumatoid arthritis who had fibromyalgia. The study showed that there was an 8.5 times higher risk that a close relative of someone with fibromyalgia had fibromyalgia than a close relative of someone with rheumatoid arthritis.(7)

Earlier I mentioned a completely genetic disease, cystic fibrosis. Cystic fibrosis is caused by a specific altered gene. What about fibromyalgia? Has a specific gene been found that causes fibromyalgia? Had fibromyalgia been caused by a change in one gene, with today’s genetic technology scientists would have found which gene it was. As with many other diseases where both genes and the environment determine the risk, the genetic risk of developing fibromyalgia depends on many genes. Probably hundreds, maybe even thousands, which all affect the risk a little bit.(5) 

Researchers know of a handful of different genes that increase the risk of fibromyalgia, but most are still unknown. If you want me to make a video about what risk-increasing genes are known, write it in the comments below.

In summary, fibromyalgia has a heritability of 50%, which means that siblings, parents, or children of people with fibromyalgia have about ten times higher risk of developing the disease. Or on average about 25% risk of getting fibromyalgia compared to 2.7% risk in the rest of the population. The risk is unevenly distributed between women and men, which a study showed where fibromyalgia was present in 14% of male close relatives of women with fibromyalgia while 41% of female close relatives had the diagnosis. This also reflects that fibromyalgia is significantly more common in women than men.

Check out my other videos about fibromyalgia and chronic pain.

References

1. Rafeeq MM, Murad HAS. Cystic fibrosis: current therapeutic targets and future approaches. J Transl Med. 2017;15:84.

2. Plomin R. Blueprint: How DNA makes us who we are. London. Penguin books:2019. 

3. Nielsen CS, Knudsen GP, Steingrímsdóttir Óa. Twin studies of pain. Clin Genet. 2012;82(4):331-40.

4. Queiroz LP. Worldwide epidemiology of fibromyalgia. Curr Pain Headache Rep. 2013;17(8):356. 

5. Park DJ, Lee SS. New insights into the genetics of fibromyalgia. Korean J Intern Med. 2017;32(6):984-95. 

6. Buskila D, Neumann L. Fibromyalgia syndrome (FM) and nonarticular tenderness in relatives of patients with FM. J Rheumatol. 1997;24(5):941-4. 

7. Arnold LM, Hudson JI, Hess EV, Ware AE, Fritz DA, Auchenbach MB. Family study of fibromyalgia. Arthritis Rheum. 2004;50(3):944-52.