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Researchers explain how serotonin is linked to somatic awareness, a condition with unexplained symptoms

People who suffer from chronic pain often report somatic awareness, a condition marked by heightened sensitivity to a variety of sensations and symptoms. These non-specific symptoms, which often include headaches, sore joints, itchy skin, constipation or shortness of breath, have no physiological explanation; nevertheless, they are enough to cause emotional distress to those who experience them.

Despite its clinical significance, scientists know very little about the etiology of somatic awareness. They only know that it manifests more often in people with naturally painful conditions, such as fibromyalgia, irritable bowel syndrome, rheumatoid arthritis and temporomandibular disorders. Research also suggests that SA increases the severity of pain felt by these individuals.

To discover how somatic awareness develops, researchers from Canada, Australia and the U.S. studied genetic data collected from a case-control cohort with orofacial pain. They looked specifically at single nucleotide polymorphisms (SNPs), which are variations in a single component of DNA known as a nucleotide, that may be unique to a person or specific to many individuals who possess a distinctive trait.

The researchers found that people who experience somatic symptoms all share a common SNP. This genetic variation lowers the activity of a particular enzyme involved in the production of serotonin, an important chemical and neurotransmitter that helps regulate mood and social behavior. The researchers reported their findings in an article published in the journal Annals of Neurology.

The link between somatic awareness and depression

Due to the lack of scientific explanation regarding the origins of somatic awareness, it is considered by many as a psychosomatic condition. However, according to Samar Khoury, a researcher at McGill University’s Alan Edwards Centre for Research on Pain and the lead author of the study, while it may sound like a fairy tale, heightened somatic awareness is real.

“Think of the fairy tale of the princess and the pea. The princess in the story had extreme sensitivity where she could feel a small pea through a pile of 20 mattresses. This is a good analogy of how someone with heightened somatic awareness might feel; they have discomforts caused by a tiny pea that doctors can’t seem to find or see, but it’s very real.”

And to prove this point, she and her team decided to look for a common denominator between people suffering from chronic jaw pain. Genetic analysis of the patients’ SNPs, particularly those whom they found to have heightened somatic awareness, revealed that all the patients carried the same genetic defect which affected their production of an enzyme called L?aromatic amino acid decarboxylase (AACD).

AACD is responsible for taking away the carboxyl groups of molecules like L-DOPA and 5-hydroxytryptophan (5-HTP). This activity is crucial for the production of the neurotransmitter, serotonin. But because of the mutation shared by people with heightened somatic awareness, their AACD enzymes function at a very slow rate, resulting in them having low levels of serotonin. Low levels of serotonin have been linked by numerous studies to depression.

“I am very happy and proud that our work provides a molecular basis for heightened somatic symptoms,” said Luda Diatchenko, a professor at McGill University and senior author of the study. She believes that their work will pave the way for future treatment options for somatic symptoms. (Related: Best natural remedies for chronic pain.)

“We believe that this work is very important to patients because we can now provide a biological explanation of their symptoms. It was often believed that there were psychological or psychiatric problems, that the problem was in that patient’s head, but our work shows that these patients have lower levels of serotonin in their blood.”

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