Antisocial Personality Disorder
Population Genetics
Family Studies
According to one family study of 223 male criminals, 80% were found to have a diagnosis of antisocial personality disorder (ASPD). Of the first-degree male relatives who were interviewed, 16% also received this diagnosis, whereas only 2% of female relatives were so diagnosed. In comparison, 3% of male control subjects and 1% of female control subjects had ASPD. Increased rates of alcoholism and drug abuse were also found among the relatives in this study.
A family study of 66 female felons and 228 of their first-degree relatives revealed increased rates of ASPD (18%), alcoholism (29%), drug abuse (3%), and hysteria (31%); all of the hysteria occurred in female relatives. Predictably, the male relatives had a threefold increase in ASPD (31%) compared to the female relatives (11%). The increased risk for ASPD among first-degree relatives of female felons (31%), compared to the risk in relatives of male felons (16%), may be related to a greater genetic loading in the families of the female felons.
Twin Studies
In a Danish twin study, 32.6% of MZ twins were concordant for criminal behavior, compared to 13.8% of DZ twins (P < .001).
Adoption Studies
Adoption studies in the 1970s reported that the adopted-away offspring of biological parents with ASPD had a higher risk for ASPD than did control adoptees. Outcome was unrelated to the length of time the adoptees remained with their biological mothers. In a study of 57 adoptee ASPD probands and 57 control probands, ASPD was found among 3.9% of biological relatives of adoptees with ASPD, compared to 1.4% of biological relatives of control adoptees, a highly significant difference. Of the biological fathers of probands, 9.3% received a diagnosis of ASPD, compared to 1.8% of the biological fathers of control adoptees.
A larger study, using adoption and criminal registries, reported that when neither the biological nor the adoptive parents had a criminal record, 13.5% of adoptees had a criminal record. If only the adoptive parents had a criminal record, the adoptee criminality rate rose to only 14.7%. If only the biological parents had a criminal record, the adoptee rate was 20%. And when both sets of parents had criminal records, the adoptee rate was 24.5%. The risk for conviction in a male adoptee increased as a function of the number of parental convictions.
These findings were confirmed in a study of criminality among a cohort of adoptees from Stockholm. The study reported that both genetic and environmental influences were detectable in the risk for ASPD. Of adoptees with a background of predisposing environmental factors, 6.7% were criminals, compared to 2.9% of male adoptees with nonpredisposing environmental and genetic backgrounds. When the genetic background, but not the environment, was predisposing, 12.1% of male adoptees were criminal, compared to 2.9% of control male adoptees. When both the genetic background and environment were judged to be predisposing, 40.0% of male adoptees were criminal. These results are consistent with the additive effects of genetic and environmental influences. Specific environmental influences implicated were multiple foster homes (for men) and extensive institutional care (for women).
Potential Biological Vulnerability Markers
Several reports have suggested that the prevalence of XYY males among the populations in prisons and in penal or mental institutions is higher than in the general population. The XYY karyotype is associated with slightly lower than normal intelligence, tall stature, and cystic acne. This karyotype is found in approximately 0.1% of male newborns but was noted in about 2% of males in penal and mental institutions. In a survey of all tall Danish men from a birth cohort, 12 out of 4139 (0.29%) had the XYY karyotype. Five of the twelve had a criminal record, involving primarily petty crimes. Lower than average intelligence may partially account for the excess of criminal activity among XYY males. This karyotype does not seem to be associated with a predisposition to impulsive violence.
A variant of the tryptophan hydroxylase gene (which codes for the synthetic enzyme for serotonin) has been associated with low 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid and with suicide attempts in violent criminal offenders. This finding deserves follow up using family-based association methods. Low 5-HIAA has been associated with impulsivity and violence in experimental colonies of rhesus monkeys and in humans.
A Dutch family was reported with lowered MAO-A activity caused by a point mutation on the eighth exon of the MAO-A gene. The males with this mutation (both MAO genes are on the X chromosome) had committed impulsive aggressive acts, arson, attempted rape, or exhibitionism. It seems likely that other familial monoamine defects may be associated with aggressive behavior.
Summary
Family, twin, and adoption studies of ASPD demonstrate that the disorder has a heritable component. This component probably includes genes that increase several characteristics associated with ASPD, including impulsivity and substance abuse. The existence of a specific genetic susceptibility to criminal acts is less certain.
