Genetics of the serotonergic system in suicidal behavior

Trauma, Genes, and the Neurobiology of Personality Disorders

A model for personality dysfunction posits an interaction between inherited susceptibility and environmental factors such as childhood trauma. Core biological vulnerabilities in personality include dimensions of affective instability, impulsive aggression, and cognition/perceptual domains. For the dimension of impulsive aggression, often seen in borderline personality disorder (BPD), the underlying neurobiology involves deficits in central serotonin function and alterations in specific brain regions in the cingulate and the medial and orbital prefrontal cortex. The role of trauma in the development of personality disorder and especially for BPD remains unclear. Although recent studies suggest that BPD is not a trauma-spectrum disorder and that it is biologically distinct from posttraumatic stress disorder, high rates of childhood abuse and neglect do exist for individuals with personality dysfunction. Personality symptom clusters seem to be unrelated to specific abuses, but they may relate to more enduring aspects of interpersonal and family environments in childhood. Whereas twin and family studies indicate a partially heritable basis for impulsive aggression, studies of serotonin-related genes to date suggest only modest contributions to behavior. Gene-environment interactions involving childhood maltreatment are demonstrated in recent studies on antisocial behaviors and aggressive rhesus monkeys and highlight the need for further research in this important area.

Polymorphisms of the tryptophan hydroxylase gene and serotonin 1A receptor gene in suicide victims among Japanese

Akita Prefecture, Japan, has consistently recorded the highest level of suicide rates in all of Japan. In this study, we attempted to determine whether genetic differences between suicide victims and the normal population in Akita exist. We also researched the geographical differences in polymorphisms of the genes between people living in Akita Prefecture and those living in other prefectures with lower suicide rates as recorded in previously-published studies. Specifically, we investigated two serotonin-related genes including three substitutions connected to human emotional states such as despondency and depression: the tryptophan hydroxylase (TPH) gene (A779C and A218C in the intron) and the serotonin1A (5-HT1A) receptor gene (Pro 16Leu in the cording region). 134 suicide victims and 325 healthy volunteers were examined. For this process, we used two analytical procedures: (1) polymerase chain reaction (PCR) followed by single-strand conformational polymorphisms analysis for the A779C of TPH and the 5-HT1A receptor genes and (2) PCR followed by restriction fragment length polymorphism analysis for the A218C of TPH gene. No significant differences of the genotypes and the allele frequencies between the suicide samples and those of the healthy controls were discerned. Moreover, the genotype distributions of the TPH and 5-HT1A receptor genes were compared between Akita Prefecture and other prefectures, but no significant differences were found. In conclusion, no significant relation could be established statistically concerning the serotonin related genes between the suicide samples and control samples in Akita.

Genome-wide linkage survey for genetic loci that affect the risk of suicide attempts in families with recurrent, early-onset, major depression

We previously described the results of a genome-wide linkage survey for genetic loci that influenced the development of unipolar mood disorders in 81 families identified by individuals with Recurrent, Early-Onset, Major Depressive Disorder (RE-MDD) [Zubenko et al. 2003b; Am J Med Genet (Neuropsychiatr Genet) 123B:1-18]. In the current study, we extended this linkage analysis by including the history of a suicide attempt as a covariate to identify chromosomal regions that harbor genes that influence the risk of this behavior in the context of mood disorders. This approach identified six linkage peaks with maximum multipoint DeltaLOD scores that reached genome-wide adjusted levels of significance (2p, 5q, 6q, 8p, 11q, and Xq). Four of these (2p, 6q, 8p, and Xq) exceeded the criterion for "highly-significant linkage" (genome-wide adjusted P < 0.001) recommended by Lander and Kruglyak [1995; Nat Genet 11:241-246]. The strongest evidence for linkage was observed in analyses employing affected relative pairs (ARPs) with the most severe and disabling Mood Disorders: Depression Spectrum Disorder and RE-MDD. The highest DeltaLOD score that emerged from this linkage analysis, 5.08, occurred for ARPs with Depression Spectrum Disorder at D8S1145 (37.0 cM, 18.2 Mbps, P < 0.0001) at cytogenetic location 8p22-p21. Significant linkage results on Xq arose from analyses of ARPs with RE-MDD at DXS1047 (143 cM, 127.8 Mbps, DeltaLOD = 3.87, P < 0.0001), a finding that may contribute to the higher rate of suicide attempts among women than men. These findings provide evidence for suicide risk loci that are independent of susceptibility loci for Mood Disorders, and suggest that the capacity for suicide risk loci to affect the development of suicidal behavior depends on the psychiatric disorder or subtype with which they interact.