The HTR2B gene, located on chromosome 2 (2q36.3-q37.1), encodes the sero tonin 2B receptor, a G protein–coupled receptor. Serotonin 2B receptors are widely expressed in the human brain. A rare HTR2B variant, namely Q20*, is associated with severe impulsivity and criminal violence in the Finnish population.131 The stop codon has an allele frequency of 1.2% among Finns, but is specific to this founder. The variant was discovered by sequencing individuals displaying extremely severe impulsive and aggressive behavior. The sequencing sample consisted of population-matched controls and violent offenders who underwent psychiatric evaluation for the extreme nature of their crimes (homicides, assaults, arsons). The variant was enriched in individuals with a history of impulsive, nonpremeditated, violence. Carriers of the stop codon who had committed violent crimes did so while inebriated with alcohol, indicating that impulsive aggression could be the result of a HTR2B stop codon by alcohol interaction. Carriers of the stop codon were cognitively within the normal range, except for a potential difference in working memory, which is known to reflect frontal lobe function. In line with studies on humans, mice
