Abstract
Objective
Heightened somatic symptoms are reported by a wide range of patients with chronic pain and have been associated with emotional distress and physical dysfunction. Despite their clinical significance, molecular mechanisms leading to their manifestation are not understood.
Methods
We used an association study design based on a curated list of 3,295 SNPs mapped to 358 genes to test somatic symptoms reporting using the Pennebaker Inventory of Limbic Languidness (PILL) questionnaire from a case‐control cohort of orofacial pain (n=1,607). A replication meta‐analysis of three independent cohorts (n=3,189) was followed by functional validation, including in silico molecular dynamics, in vitro enzyme assays, and measures of serotonin (5‐HT) plasma concentration.
Results
An association with T allele of rs11575542 coding for an arginine to glutamine substitution in the L‐aromatic amino acid decarboxylase (AADC) enzyme was replicated in a meta‐analysis of three independent cohorts. In a combined meta‐analysis of all cohorts this association reached p=6.43x10‐8. In silico studies demonstrated that this substitution dramatically reduces the conformational dynamics of AADC, potentially lowering its binding capacity to a co‐factor. In vitro enzymatic assays showed that this substitution reduces the maximum kinetic velocity of AADC, hence lowering serotonin (5‐HT) levels. Finally, plasma samples from 90 subjects showed correlation between low 5‐HT levels and heightened somatic symptoms.
Interpretation
Thus, using functional genomics approaches, we identified a polymorphism in AADC enzyme that contributes to somatic symptoms through reduced levels of 5‐HT. Our findings suggest a molecular mechanism underlying the pathophysiology of somatic symptoms and opens up new treatment options targeting the serotonergic system.
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