Serotonin-related gene pathways associated with undifferentiated somatoform disorder

Genetics of Functional Seizures; A Scoping Systematic Review

BACKGROUND

Evidence on the genetics of functional seizures is scarce, and the purpose of the current scoping systematic review is to examine the existing evidence and propose how to advance the field.

METHODS

Web of science and MEDLINE were searched, from their initiation until May 2023. The following key words were used: functional neurological disorder(s), psychogenic neurological disorder(s), functional movement disorder(s), psychogenic movement disorder(s), functional seizures(s), psychogenic seizure(s), nonepileptic seizure(s), dissociative seizure(s), or psychogenic nonepileptic seizure(s), AND, gene, genetic(s), polymorphism, genome, epigenetics, copy number variant, copy number variation(s), whole exome sequencing, or next-generation sequencing.

RESULTS

We identified three original studies. In one study, the authors observed that six (5.9%) patients with functional seizures carried pathogenic/likely pathogenic variants. In another study, the authors observed that, in functional seizures, there was a significant correlation with genes that are over-represented in adrenergic, serotonergic, oxytocin, opioid, and GABA receptor signaling pathways. In the third study, the authors observed that patients with functional seizures, as well as patients with depression, had significantly different genotypes in FKBP5 single nucleotide polymorphisms compared with controls.

CONCLUSION

Future genetic investigations of patients with functional seizures would increase our understanding of the pathophysiological and neurobiological problems underlying this common neuropsychological stress-associated condition.

Effects of TPH2 gene variation and childhood trauma on the clinical and circuit-level phenotype of functional movement disorders

BACKGROUND

Functional movement disorders (FMDs), part of the wide spectrum of functional neurological disorders (conversion disorders), are common and often associated with a poor prognosis. Nevertheless, little is known about their neurobiological underpinnings, particularly with regard to the contribution of genetic factors. Because FMD and stress-related disorders share a common core of biobehavioural manifestations, we investigated whether variants in stress-related genes also contributed, directly and interactively with childhood trauma, to the clinical and circuit-level phenotypes of FMD.

METHODS

Sixty-nine patients with a 'clinically defined' diagnosis of FMD were genotyped for 18 single-nucleotide polymorphisms (SNPs) from 14 candidate genes. FMD clinical characteristics, psychiatric comorbidity and symptomatology, and childhood trauma exposure were assessed. Resting-state functional connectivity data were obtained in a subgroup of 38 patients with FMD and 38 age-matched and sex-matched healthy controls. Amygdala-frontal connectivity was analysed using a whole-brain seed-based approach.

RESULTS

Among the SNPs analysed, a tryptophan hydroxylase 2 (TPH2) gene polymorphism-G703T-significantly predicted clinical and neurocircuitry manifestations of FMD. Relative to GG homozygotes, T carriers were characterised by earlier FMD age of onset and decreased connectivity between the right amygdala and the middle frontal gyrus. Furthermore, the TPH2 genotype showed a significant interaction with childhood trauma in predicting worse symptom severity.

CONCLUSIONS

This is, to our knowledge, the first study showing that the TPH2 genotype may modulate FMD both directly and interactively with childhood trauma. Because both this polymorphism and early-life stress alter serotonin levels, our findings support a potential molecular mechanism modulating FMD phenotype.

Epigenetics-by-sex interaction for somatization conferred by methylation at the promoter region of SLC6A4 gene

BACKGROUND

Depression, anxiety and somatoform disorders are all more prevalent in women than in men. However, specific biological mechanisms contributing to such sex differences remain unknown. Serotonergic pathways are involved in mood and behavior regulation and thus have been suggested to be altered in several psychiatric disorders. The serotonin transporter (SERT), encoded by SLC6A4 gene, has received major attention due to its crucial role in serotonergic transmission.

METHODS

148 monozygotic twin subjects were assessed for (i) lifetime categorical diagnosis of anxious-depressive disorders, following SCID-I-based DSM-IV criteria, and (ii) current psychiatric symptomatology, from a dimensional approach, by means of the Brief Symptom Inventory (BSI). SLC6A4 gene methylation was analyzed by means of Infinium HumanMethylation450 in a subset of the sample. CpG-specific methylation at the promoter region of SLC6A4 gene was further analyzed by means of pyrosequencing technology in the total sample.

RESULTS

SLC6A4 methylation was found to be significantly higher in women when compared to men independent of DSM-IV diagnosis. SLC6A4 methylation was further associated with the BSI-derived somatization dimension.

CONCLUSIONS

Female hypermethylation of a discrete region located within SLC6A4 promoter region could underlie differential SERT expression in women when compared to men and could be one of the causative mechanisms by which women exhibit increased prevalence of somatic symptoms.

Decreased Plasma BDNF Levels of Patients with Somatization Disorder

OBJECTIVE

Brain-derived neurotrophic factor (BDNF), one of the most abundant and important neurotrophins, is known to be involved in the development, survival, maintenance, and plasticity of neurons in the nervous system. Some studies have suggested that BDNF may play a role in the pathophysiology of several psychiatric illnesses such as depression and schizophrenia. Similarly, it is likely that the alteration of BDNF may be associated with the neuro-modulation that contributes to the development of somatization disorder.

METHODS

The purpose of this study was to determine whether there is an abnormality of plasma BDNF levels in patients with somatization disorder, and to analyze the nature of the alteration after pharmacotherapy using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The plasma BDNF levels of the patients with a somatization disorder were significantly lower compared with those of the control volunteers (83.61±89.97 pg/mL vs. 771.36±562.14 pg/mL); moreover, the plasma BDNF levels of those patients who received an antidepressant were significantly increased after the treatment (118.13±91.45 pg/mL vs. 72.92±88.21 pg/mL).

CONCLUSION

These results suggest that BDNF may play a role in the pathophysiology of somatization disorder.

Somatization severity associated with postero-medial complex structures

Somatisation is a frequent problem in various psychiatric disorders, yet the cerebral mechanisms of somatisation remain unexamined. To test if somatisation is susceptible to emotional states, we investigated relationships between somatisation severity, neural effective connectivity, and autonomic responses to emotional facial expressions. Volunteering participants (N = 20) were presented with facial expressions of happy and sad emotion at three intensity levels (0%–50%–100%) in a fast implicit ER-fMRI design with concurrent derivation of skin conductance levels (SCL). Self-reported somatisation severity as assessed with Rief's SOMS-2 index was correlated with neural response controlling for other clinical traits to ascertain brain bases of somatisation. Regression analyses estimated effective connectivity of main clusters so determined with peripheral autonomic responses. Regions in which magnitude of activity correlated with somatisation severity consisted in both happy and sad conditions of the anterior ventral precuneus (BA7), along with posterior cingulate gyrus (PCC, BA23, sad condition) and anteromedial thalamus (happy condition).

[Etiopathogenetic aspects of somatoform disorders]

The etiopathology of somatoform disorders can only be understood against the background of an integrated biopsychosocial model. Cultural and historical influences must be taken into account as well as contemporary settings of scientific or medical priorities. In this context the emphasis on neurobiological findings can be interpreted as the non-accidental struggle for legitimacy of both patients and physicians. Altogether the available data on factors influencing the formation and maintenance of somatoform symptoms has to be described as both diverse and unspecific and thus points to a challenging research program in the coming years.