Variants in TPH2 and ADARB1 genes in completed suicide from the Slovenian population – a follow-up to findings on attempted suicide in the Serbian population

Suicidal behaviour, including completed suicide and attempted suicide, is affected by genetic factors, involving serotonergic system genes. TPH2 gene encodes tryptophan hydroxylase 2, rate-limiting brain serotonin synthetising enzyme whose pre-mRNAs are edited by ADAR enzymes, including ADARB1. TPH2 rs4290270 and ADARB1 rs9983925/rs4819035 variants have been previously implicated in suicide attempt in Serbian psychiatric patients. Our aim was to investigate whether these variants could also contribute to genetic predisposition for a more extreme phenotype-completed suicide differentiated by violent and non-violent method-in a Slovenian cohort. Genotyping of TPH2 rs4290270 and ADARB1 rs9983925/rs4819035 was performed on sample including 333 suicide completers (305 violent and 28 non-violent), and 357 non-suicidal autopsy controls from Slovenia. Statistical analyses were performed in PLINK ver. 1.9. TPH2 rs4290270 AA genotype increased the risk of completed suicide compared to controls (p = 0.032/0.031corrected), mainly driven by violent suicide (p = 0.045/0.044corrected). Preliminary, ADARB1 rs4819035 GT and GG genotypes increased the risk of non-violent completed suicide compared to controls (p = 0.015/0.011corrected), and to violent completed suicide (p = 0.026/0.022corrected). TPH2 and ADARB1 genetic variants shape different genetic backgrounds in different types of suicidal behaviour, completed and attempted suicide. Preliminary, these variants might also differentiate between various methods of completed suicide, violent and non-violent.