Cukrowicz, K.C., Taylor, J., Schatschneider, C. & Iacono, W.G. (2006). Personality Differences in Children with Attention-Deficit/Hyperactivity Disorder, Conduct Disorder and Controls. Journal of Child Psychology and Psychiatry, 47, 151-159.

Background: Differences in personality profiles were examined between children who differed in their co-morbidity of externalizing disorders: attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD).
Methods: 11- and 17-year-old male and female twins from a community sample were categorized as ADHD only, CD only, co-morbid CD-ADHD, and controls (no ADHD or CD) based on threshold and subthreshold CD and ADHD diagnoses assessed with structured interviews. Multivariate analyses were used to identify patterns of personality that differentiate these four diagnostic groups. It was hypothesized that significant differences would be found in the pattern of personality variables between participants in the co-morbid group, compared to the other three groups, and that these differences would hold across developmental periods.
Results: As expected, the co-morbid group had a pattern of personality marked by higher Negative Emotionality and lower Constraint than the other diagnostic groups. This pattern was evidenced across gender and age cohort.
Conclusions: An extreme personality profile may represent a liability toward the occurrence of ADHD and CD with more extreme profiles contributing to the occurrence of both disorders among boys and girls. Implications for treatment planning and theoretical development are discussed.

Sherman, D. K., M. K. McGue, et al. (1997). "Twin concordance for attention deficit hyperactivity disorder: a comparison of teachers' and mothers' reports." Am J Psychiatry 154(4): 532-5.

The present study examined probandwise concordance rates for attention deficit hyperactivity disorder (ADHD) in a community sample of 194 monozygotic and 94 dizygotic male twins, ages 11-12 years. METHOD: DSM-III and DSM-III-R diagnoses of ADHD were based on rating scale reports from the twins' teachers and structured interview reports obtained from their mothers. Model-fitting analyses were used to estimate genetic and environmental effects on ADHD. RESULTS: Concordance rates for ADHD were greater for monozygotic than dizygotic twins according to both mothers' and teachers' reports; this finding indicates the importance of genetic factors in the etiology of this syndrome. Fifteen percent of subjects received an ADHD diagnosis by teachers' ratings, compared with 6% by mothers' reports. Three percent of subjects met criteria for ADHD in both school and home settings. Teachers' ratings yielded moderate monozygotic and dizygotic concordance rates, in contrast to mothers' reports, which indicated a high monozygotic and a zero dizygotic concordance for ADHD. A model that included additive genetic and nonshared environmental factors provided the best fit to these ADHD data. CONCLUSIONS: ADHD, as defined by DSM criteria, appears to be a genetically influenced disorder whether diagnoses are based on teachers' or mothers' reports. However, the extent of this genetic influence seems to vary by informant source. These findings suggest that obtaining diagnostic data from either teachers' or mothers' reports alone may provide an incomplete characterization of ADHD.

Sherman, D. K., W. G. Iacono, et al. (1997). "Attention-deficit hyperactivity disorder dimensions: a twin study of inattention and impulsivity-hyperactivity." J Am Acad Child Adolesc Psychiatry 36(6): 745-53.

This study used a model-fitting strategy to estimate genetic and environmental contributions to the core behavioral dimensions associated with attention-deficit hyperactivity disorder (ADHD) in 576 twin boys, aged 11 and 12 years. METHOD: Teacher ratings and maternal structured interview reports composed of behavioral items including DSM- III and DSM-III-R criteria for ADHD were obtained for 194 pairs of monozygotic and 94 pairs of dizygotic twins. Factor analysis of these measures yielded two ADHD-related dimensions, inattention and impulsivity-hyperactivity. Scales representing these dimensions were used in the genetic analyses. RESULTS: Univariate analyses supported a substantial contribution of genetic factors in the expression of inattention and impulsivity-hyperactivity and smaller contributions of shared and nonshared environmental factors. Results varied according to informant source, with mothers' reports suggestive of rater bias effects. Bivariate analyses indicated that the correlation between these two ADHD dimensions was also genetically mediated. CONCLUSIONS: Genetic factors are etiologically important in the expression of the separate dimensions of ADHD and in the covariation between them. However, it is important to obtain reports from more than one informant because rater bias effects may be operative, particularly in maternal reports.


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