Genetics seem to be play a larger role in driving the development of fibromyalgia in patients, 50 or younger, than in those who are older and more likely to have the condition with an accompanying disorder, or secondary fibromyalgia, a study suggests.
These results highlight the importance of taking age into account when studying the genetics of fibromyalgia, the researchers stated.
Their study, “Heritability of the fibromyalgia phenotype varies by age,” was published in the journal Arthritis & Rheumatology.
Although fibromyalgia (FM) is not passed directly from parents to children, many studies suggest a strong familial component. In fact, DNA studies comparing the genetic background of people with FM and healthy controls have found some genes that may increase susceptibility to fibromyalgia, but such results have been inconsistent.
Moreover, the studies performed to date have been small in size and have also been limited to individuals with primary FM, meaning fibromyalgia without any other accompanying conditions.
Primary FM typically begins early in life, causing the first symptoms of pain during childhood or adolescence. It occurs more often in females and is associated with other regional pain conditions in individuals and families.
Recognizing that, a team of researchers from Johns Hopkins and the University of Michigan, set out to estimate the heritability, or genetic predisposition, of FM and to see if this heritability depended on a person’s sex or age.
They collected data on 26,749 adult individuals of European ancestry enrolled in the Michigan Genomics Initiative (MGI), at the University of Michigan.
The researchers collected DNA from blood samples of participants and estimated their genetic predisposition to develop FM using a genome-wide association study (GWAS).
GWAS is a method that searches the genome for small variations, which occur more frequently in people with a given disease than in people without the disease. Researchers use this data to identify genes that may increase a person’s risk of developing a certain condition.
The researchers used a continuous measure of FM severity, the FM score, to identify people with the condition. This tool is based on the current 2011-16 criteria for diagnosing FM and combines a measure of painful sites in the body with the severity of other symptoms (fatigue, trouble thinking or remembering, waking up tired, pain or cramps in the lower abdomen, depression, and headache).
The results showed that overall estimated FM heritability was 13.9%, meaning that 13.9% of the odds of developing FM could be explained by genetic risk.
However, differences were noted across age groups. Younger individuals appeared to have a much stronger genetic component driving the development of FM than older individuals.
Estimated FM-score heritability was greater in individuals who developed the disease when they were 50 or younger (23.5% ) and was lowest in individuals whose disease emerged after age 60 (7.3%).
No significant differences were seen between men and women, although women had approximately 30% higher FM scores than males across ages.
“These data support the distinction that there are (at least) two different forms of FM: one that occurs in younger individuals and is strongly genetically driven — and the other that occurs in older individuals and can be driven by a variety of non-genetic factors and other conditions that cause pain,” the researchers wrote.
Older individuals may be more likely to have what’s known as secondary FM, they said.
“Older individuals may have a greater contribution of environmental factors to pain, a greater diversity of conditions that increase pain, and/or more susceptibility towards nociceptive pain” (pain from inflammation or injury), they wrote.
The study also highlights “the importance of considering the age distribution of individuals when designing a genetic association study of FM.”
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