Fibromyalgia is characterized by spontaneous and widespread pain and affects millions worldwide. There is evidence that the condition is more prevalent among women than men (by about seven to nine times) and is seen to run in families. It is thus speculated that there may be certain genetic abnormalities that may predispose to fibromyalgia.
Fibromyalgia in specific gene clusters
There are studies that look at the risk or odds of fibromyalgia in specific gene clusters. It suggests that the number of tender points is significantly higher in relatives of fibromyalgia patients when compared to relatives of patients suffering from rheumatoid arthritis.
Fibromyalgia in first-degree relatives
The frequency of fibromyalgia among the first-degree relatives of those with a genetic makeup of fibromyalgia and rheumatoid arthritis is around 6.4% and 1.1%, respectively.
The median number of tender points among the first-degree relatives of the fibromyalgia patients was 17 out of maximum of 18.
Fibromyalgia and ethnic groups
Fibromyalgia has been additionally investigated among various ethnic groups. Studies have shown a particular prevalence in rural communities compared to urban populations.
Patients of non-Hispanic Caucasian or Asian descent are at a greater risk. The rural urban differences are seen among several South East Asian countries as well.
Genes implicated in fibromyalgia
Early genetic studies connecting genes to fibromyalgia showed that there are high levels of the DR4 antigen in 64% versus 30% among healthy controls. Fibromyalgia is also linked significantly to the HLA region.
Studies have revealed association of genes involved in the metabolism of serotonin with fibromyalgia. The most commonly studied gene in this respect is the serotonin transporter gene (5-HTT) promoter region in ﬁbromyalgia.
Results showed an increased frequency of the S/S genotype of the 5-HTT gene among patients of fibromyalgia compared to healthy controls.
However, no similar association was found when studying T102C polymorphism of the 5-HT2A-receptor gene. This is another serotonin receptor candidate gene.
No association was found between fibromyalgia and serotonin receptor subunit genes, HTR3A and HTR3B as well.
Another area of investigation is the connection of fibromyalgia with the catechol-O-methyltransferase (COMT) gene variants. The COMT gene encodes an enzyme that metabolizes catecholamines (i.e., norepinephrine and dopamine). It thus influences several modalities of pain perception and sensitivity.
COMT also has been implicated in the pathogenesis of migraine and anxiety disorders. There is an association of fibromyalgia with COMT gene alteration as well.