Serotonin Levels May Clarify Unexplained Pain

A newly-discovered biological mechanism could explain heightened somatic awareness, in which people experience pain that has no physiological explanation.

Patients with heightened somatic awareness often experience unexplained symptoms — headaches, sore joints, nausea, constipation, or itchy skin — that cause emotional distress, and are twice as likely to develop chronic pain. The condition, associated with illnesses such as fibromyalgia, rheumatoid arthritis, and temporomandibular disorders, is thought to have a psychological origin.

“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,”

says Samar Khoury, a postdoctoral fellow at the Alan Edwards Centre for Research on Pain at McGill University.

Somatic Awareness

Thanks to an existing study on genetic association, Khoury and her colleagues might have found the elusive pea that explains somatic awareness.

The researchers used data available through the Orofacial Pain: Prospective Evaluation and Risk Assessment cohort that demonstrates that patients who suffer from somatic symptoms share a common genetic variant. The mutation leads to the malfunctioning of an enzyme critical for the production of serotonin, a neurotransmitter with numerous biological functions.

“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,”

says lead author Luda Diatchenko, a professor in the Faculty of Dentistry.

Next Steps

The results of the study lay the groundwork for the development of animal models that could better characterize the molecular pathways in heightened somatic awareness. Above all, Diatchenko and Khoury hope the work will pave the way for treatment options.

“The next step for us would be to see if we are able to target serotonin levels in order to alleviate these symptoms,”

says Diatchenko, who holds the Canada Excellence Research Chair in Human Pain Genetics.

The work was supported by Canadian Institutes of Health Research, Natural Sciences and Engineering Research Council of Canada, the National Institutes of Health, and the National Institute of Dental and Craniofacial Research.

Khoury, S. , Piltonen, M. H., Ton, A. , Cole, T. , Samoshkin, A. , Smith, S. B., Belfer, I. , Slade, G. D., Fillingim, R. B., Greenspan, J. D., Ohrbach, R. , Maixner, W. , Neely, G. G., Serohijos, A. W. and Diatchenko, L.
A functional substitution in the L‐aromatic amino acid decarboxylase enzyme worsens somatic symptoms via a serotonergic pathway
Ann Neurol. doi:10.1002/ana.25521

Image: Chris Nurse, Wellcome Images


Did you like this article? Then you'll really want to sign up for my newsletter. It's delivered several times a week and packed with science news and analysis. Subscribe Here.