The studies reviewed thus far have focused on genetic variation in common SNPs, where the frequency of the minor allele is typically greater than 1%. Other forms of genetic variation may also contribute to the heritability of conduct disorder. In particular, there has been a growing interest in variants that are likely to be highly deleterious (and thus rare, with a minor allele frequency of less than 1%) located in the exome, which is the protein-coding portion of the genome. There are now cost effective methods to conduct systematic tests of association for rare variant exonic SNPs. Although there has not yet been a rare variant association study of conduct disorder diagnoses or symptom counts, there has been a study of a closely related behavioral disinhibition phenotype, which included antisocial and dissocial behaviors. In a sample of 7,181 individuals, approximately 100,000 rare (minor allele frequency < 0.05) non-synonymous exonic SNPs were examined for association with the behavioral disinhibition phenotype (Vrieze et al., 2014). In aggregate, these SNPs accounted for 14% of the variance in behavioral disinhibition (p = 0.05). However, no significant associations emerged from SNP and gene-based burden tests of association.
