The first of the studies was performed in human subjects of both genders (with a sample of roughly 1,000 individuals), following them across multiple time points throughout their lives, and demonstrated that a low-functioning allele of monoamine oxidase A (MAO-A) was associated with numerous adverse outcomes later in life, relating particularly to conduct disorder, antisocial personality disorder, violence, and incarceration [15]. This evidence concerns the gene MAOA and conduct disorder.