The heritability and comorbidity of attention deficit hyperactivity disorder (ADHD) with conduct disorder (CD), oppositional defiant disorder (ODD), and executive function (EF) deficits were examined in 224 child twins (140 monozygotic and 84 dizygotic). The Coolidge Personality and Neuropsychological Inventory for Children (Coolidge, 1998), a standardized, 200-item, Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) aligned, parent-as-respondent inventory, assessed psychopathology. Structural equation model fitting revealed that the individual scale heritabilities were substantial: .82 for ADHD, .74 for CD, .61 for ODD, and .77 for EF deficits. The results of the multivariate twin analyses suggest that ADHD shares most of its genetic liability with CD, ODD, and EF deficits. Thus, the findings argue for a common biological risk underlying these commonly comorbid externalizing behavior problems and cognitive deficits. The residual genetic variance provides preliminary support for additional genetic influences underlying CD, ODD, and EF that are independent of ADHD.

The heritability of personality disorder features was investigated in 112 child (ages 4-15 years) twin pairs (70 monozygotic and 42 dizygotic pairs). Parents assessed personality disorder features using the Coolidge Personality and Neuropsychological Inventory for Children (CPNI; Coolidge, 1998) that measures 12 personality disorders according to the criteria in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American Psychiatric Association, 1994). Structural equation model-fitting methods indicated that the median heritability coefficient for the 12 scales was .75 (ranging from .81 for the Dependent and Schizotypal Personality Disorder scales to .50 for the Paranoid and Passive-Aggressive Personality Disorder scales). These results suggest that childhood personality disorders have a substantial genetic component and that they are similar to heritability estimates of personality disorder traits in adults and counter hypotheses that only temperaments and higher-order personality disorder traits have significant genetic components (Paris, 1997).

This study describes the preliminary psychometric characteristics of a new parent-as-respondent assessment tool, the Coolidge Personality and Neuropsychological Inventory for Children (CPNI). The CPNI contains 200 items answered on a 4-point Likert-type scale. The CPNI has a three-fold purpose: (a) to assess the 12 personality disorders according to the criteria on Axis II and Appendix B of the Diagnostic and Statistical Manual of Mental Disorders; (b) to assess neuropsychological dysfunction, including Attention-Deficit/Hyperactivity Disorder, Mild Neurocognitive Disorder, executive function deficits, and other related symptoms; and (c) to measure some Axis I diagnoses including Separation Anxiety Disorder, Oppositional Defiant Disorder, depression, and general anxiety, as well as other clinical syndromes. The scale reliabilities and test-retest reliabilities were moderate to high, and construct validity was good, which supports further research with the inventory.

This study tested whether personality disorders may be the psychological manifestations of executive function deficits by examining their bivariate heritability in a community sample of 314 twins (ages 5-17 years; M age = 9.7; 96 monozygotic pairs and 61 dizygotic pairs). The parents of the twins completed the Coolidge Personality and Neuropsychological Inventory (Coolidge, 1998; Coolidge et al., 2002). Heritability was estimated by structural equation modeling. Executive function deficits and personality disorders were significantly heritable (executive function deficits,.77; 11 out of 12 personality disorders, median =.69). The proportion of the observed correlation attributable to heritable factors or bivariate heritability between executive function deficits and the personality disorder scales ranged from.27 for schizoid to.64 for histrionic. These findings may provide some insight as to why individuals diagnosed with specific personality disorders frequently exhibit chronic difficulties with everyday decisions, selective attention and inhibition, judgments, choices, planning, and flexibility.

This study investigated personality and neurobehavioral differences between 16 children with Asperger's Disorder, 15 children with High-Functioning Autism (HFA), and 31 controls, all ranging in age from 5-17 years, M age = 10.7 years, SD = 3.0. Parents rated their children's behaviors on a 44-item autistic symptoms survey and on the 200-item Coolidge Personality and Neuropsychological Inventory (Coolidge, Thede, Stewart, & Segal (2002a). The Coolidge Personality and Neuropsychological Inventory for Children (CPNI): Preliminary psychometric characteristics. Behavior Modification, 26, 550-566). The results indicated that the two clinical samples were significantly elevated on the Executive Function Deficits scale and Attention-Deficit/Hyperactivity Disorder (ADHD) scale compared to controls. There were more similarities than differences between the two clinical samples on the personality scales, although the Asperger's group scored significantly on the two scales with anxiety components.