Aggression is perceived as hostile, injurious, or destructive behavior often caused by frustration, can be collective or individual. Genetic studies have associated several genes with aggression in humans. One of the candidate genes that turned out to be associated with aggression, anger, and impulsivity is the tryptophan hydroxylase (TPH) gene. We investigated the polymorphism in the TPH gene in the unrelated male individuals in the Punjab ethnic backgrounds who were administered the Punjabi translation of Buss and Perry aggression questionnaire. The questionnaire measured four aspects of aggression: physical aggression, verbal aggression, anger and hostility (Buss and Perry, 1992).Scores ± SD of 83.544± 26.63 was obtained for Buss and Perry aggression questionnaire. TPH is a rate-limiting biosynthetic enzyme in the serotonin pathway and regulates levels of 5-hydroxytryptophan (5-HT) by converting tryptophan into 5-hydroxytryptophan, which is the direct precursor of 5-HT.
It is conceivable that variations in the TPH gene could contribute to low activity of the 5-HT system. Single nucleotide polymorphisms (SNPs) that show associations to aggression and anger-related traits have been detected in intron 7 of TPH gene.DNA of individuals categorized into controls and criminal groups was extracted by organic method of DNA extraction.The targeted region of the TPH gene was amplified by the primers designed against intron seven. The amplified Pcr product was precipitated and it was sent for sequencing. The resultant sequenced data was then compared on the basis of Buss and Perry aggression scores. All unrelated male individuals from the Punjab ethnic groups were assessed on the scales showing scores for physical aggression, verbal aggression, anger and hostility. The minimum score for the respondents were 65 and highest score for the respondents were 135 among the criminal group while control have minimum scores of 50 and maximum scores of 113.Mean scores and standard deviations were calculated for criminals and control groups. Control group havephysical aggressionmean scores ± SD19.318 ± 6.21, verbal aggressionmean scores ± SD17.590± 4.41,angermean scores ± SD23 ± 6.868and hostility mean scores ± SD23.636± 9.12and total mean scores ± SD83.544± 26.63while criminals have physical aggressionmean scores ± SD28.2±8.134, verbal aggressionmean scores ± SD20.4±4.427, anger mean scores ± SD27.3±6.97and hostilitymean scores ± SD28.1±7.72and totalmean scores ± SD04.2±20.47.Mean aggression values for the criminals was 104 and for controls was 83, higher in criminals as expected. Criminals groups exhibited greater level of aggression as compared to that of control groups on the basis of four scales of aggression i.e. physical aggression, verbal aggression, anger and hostility.
Observed genotypic frequencies among the control groups were 0.7 for CC, 0.3 for the AC and 0 for AA whereas genotypic frequencies amongst criminal group were 0.3 for CC, 0.6 for AC and 0.1 for AA. Controls carried higher genotypic frequencies for normal CC genotype than criminals whereas the genotypic frequencies for AA and AC genotypes were higher in Criminal group.Observed allelic frequencies amongst the control group was 0.8 for C and 0.15 for A whereas observed allelic frequencies amongst the criminal group was 0.4 for A and 0.6 for C. Controls carried higher allelic frequencies for the normal C allele while criminals carried higher allelic frequencies for A allele.In our study proportion of the less common (A or U) alleles was 40%, and the proportion of the more common (C or L) alleles was 60% in criminal group as compared to 15% of A allele and 85% of C allele in the control group. Statistical analysis has associated significantly Criminals and controls group at P value less than 0.05.
Advances in the understanding of the genes modulating aggression can contribute meaningfully to a rational assessment and treatment of individuals with pathological aggression and a predisposition to violence. Results can be utilized for the screening of Aggression in the individuals for forensic applications. In future studies, other polymorphism in TPH and other aggression related genes may also be analysed in Pakistani population.