PEDIGREE ANALYSIS OF SUICIDAL BEHAVIOUR ACCUMULATION WITHIN FAMILY

We found no studies that investigated the mode of inheritance of suicidal behaviour (SB) using a clinical and genealogical method. The study aim was to analyse a clinical and genealogical case-control study of familial inheritance and accumulation of SB to demonstrate that the inheritance of SB is multifactorial. Material and Methods. Genealogical data were collected between February and May 2024 by direct interview of relatives of the proband alive at the time of examination. In total, eight generations were traced. The pedigree included 127 individuals, a total of 61 males and 66 females, 82 of whom were blood relatives of the proband. The incidence of SB, including both completed suicide and non-lethal suicide attempts (parasuicide), was assessed. Cases of incomplete suicide were counted as parasuicide. Zygosity due to the apparent multifactorial inheritance of SB was not determined. The genealogical tree of the proband was constructed according to generally accepted recommendations. The study was conducted exclusively on the voluntary basis of the proband and his relatives. Personal and geographical data that could identify the proband and/or his relatives were excluded from the results of the study. The numerical data obtained were used to calculate the incidence of SB and penetrance using conventional methods. The relative risk and odds ratio of inheriting SB, committing suicide and/or parasuicide were calculated. The heritability of SB was assessed by regression analysis. Data are presented as M +/- m, where M is the mean of the notional estimate and m is the standard error. A p<0.05 was considered statistically significant. Results. SP was observed in almost every generation on both the maternal and paternal sides. Among the proband's blood siblings, SB occurred in 6 males (4 suicides and 2 parasuicides) and 21 females (5 suicides and 16 parasuicides), penetrance 31.71%, not complete. Among non-blood relatives, there were 2 male and 3 female suicides and 2 female parasuicides. The relative risk of inheriting SB without sex was 2.963 (95% CI 1.2267.164), p=0.0158, 1.737 (95% CI 0.383-7.876) p=0.4741 for males and 2.823 (95% CI 1.256-6.346), p=0.0121 for females. The probability of inheriting the SB phenotype independent of sex OR=3.93; 95% CI 1.39-11.08; chi(2)=7.34, p<0.01, F=0.0096. Odds of parasuicide by a female sibling OR=6.96; 95% CI 1.42-34.03; chi(2)=6.90, p<0.01, F=0.0094, male OR=1.25; 95% CI 0.21-7.46, chi(2)=0.06, p>0.05, F=0.9999. The odds of a female sibling committing suicide OR=4.17; 95% CI 0.45-38.66; x2=1.8, p>0.05, F=0.3803, male OR=1.25; 95% CI 0.11-14.7; chi(2)=0.03, p>0.05, F=0.9999. Regression analysis showed that SP inheritance was linearly associated with sex (beta 1=0.29, (beta 2=0.2, p=0.001) and negatively associated with consanguinity (beta 1=-0.23, (beta 2=-0.15, p=0.0107). It is concluded that: 1) the inheritance of suicidal behaviour is multifactorial, polygenic, dominant with incomplete penetrance; 2) due to genetic heterogeneity of the gene network formed by many polymorphic genes, phenotypes of suicidal behaviour may differ in terms of external behavioural attributes of suicidal behaviour and outcomes.