Fibromyalgia largely overlaps with chronic fatigue syndrome and may share the same pathogenetic mechanisms. Comorbid fibromyalgia has been reported to occur in 20–30% of individuals with rheumatic diseases. It has been reported in people with noninflammatory musculoskeletal diseases. The prevalence of fibromyalgia in gastrointestinal disease has been described mostly for celiac disease and irritable bowel syndrome (IBS). IBS and fibromyalgia share similar pathogenic mechanisms, involving immune system mast cells, inflammatory biomarkers, hormones, and neurotransmitters such as serotonin. Changes in the gut biome alter serotonin levels, leading to autonomic nervous system hyperstimulation. Fibromyalgia has also been linked with obesity. Other conditions that are associated with fibromyalgia include connective tissue disorders, cardiovascular autonomic abnormalities, and an overactive bladder. Risk factors The cause of fibromyalgia is unknown. However, several risk factors, genetic and environmental, have been identified. Genetics Genetics play a major role in fibromyalgia, and may explain up to 50% of the disease susceptibility. Fibromyalgia is potentially associated with polymorphisms of genes in the serotoninergic, dopaminergic and catecholaminergic systems. Several genes have been suggested as candidates for susceptibility to fibromyalgia. These include SLC6A4, TRPV2, MYT1L, NRXN3, and the 5-HT2A receptor 102T/C polymorphism. The heritability of fibromyalgia is estimated to be higher in patients younger than 50. Neuropathic pain and major depressive disorder often co-occur with fibromyalgia – the reason for this comorbidity appears to be due to shared genetic abnormalities, which leads to impairments in monoaminergic, glutamatergic, neurotrophic, opioid and proinflammatory cytokine signaling. In these vulnerable individuals, psychological stress or illness can cause abnormalities in inflammatory and stress pathways that regulate mood and pain. Eventually, a sensitization and kindling effect occurs in certain neurons leading to the establishment of fibromyalgia and sometimes a mood disorder. Stress Stress may be an important precipitating factor in the development of fibromyalgia. A 2021 meta-analysis found psychological trauma to be strongly associated with fibromyalgia. People who suffered abuse in their lifetime were three times more likely to have fibromyalgia, people who suffered medical trauma or other stressors in their lifetime were about twice as likely. Some authors have proposed that, because exposure to stressful conditions can alter the function of the hypothalamic-pituitary-adrenal (HPA) axis, the development of fibromyalgia may stem from stress-induced disruption of the HPA axis. Personality Although some have suggested that fibromyalgia patients are more likely to have specific personality traits, when depression is statistically controlled for, it appears that their personality is no