Aside from findings related to neurological and neurochemical profiles of youth with conduct disorder, intraindividual factors such as genetics may also be relevant. Having a sibling or parent with conduct disorder increases the likelihood of having the disorder, with a heritability rate of .53.[34] There also tends to be a stronger genetic link for individuals with childhood-onset compared to adolescent onset.[35] In addition, youth with conduct disorder also exhibit polymorphism in the monoamine oxidase A gene,[36] low resting heart rates,[37] and increased testosterone.[38]