Attention-Deficit/Hyperactivity Disorder and Comorbid Disruptive Behavior Disorders: Evidence of Pleiotropy and New Susceptibility Loci

Background Attention-deficit/hyperactivity disorder (ADHD) comorbid with oppositional defiant disorder (ODD) or conduct disorder (CD) and substance abuse/dependence seems to represent a specific subset within the phenotypic ADHD spectrum. Methods We applied complex segregation and linkage analyses in a set of multigenerational families densely segregating ADHD comorbid with ODD, CD, alcohol abuse/dependence, and nicotine dependence. Results Our data suggest that ADHD cosegregates with disruptive behaviors as a unique, phenotypically variable trait as evidenced by highly significant pair-wise linkages among: ADHD and ODD (logarithm of odds [LOD] = 14.19), ADHD and CD (LOD = 5.34), ODD and CD (LOD = 6.68), and CD and alcohol abuse/dependence (LOD = 3.98). In addition to previously reported ADHD susceptibility loci, we found evidence of linkage for comorbid ADHD phenotypes to loci at 8q24, 2p21-22.3, 5p13.1-p13.3, 12p11.23-13.3, 8q15, and 14q21.1-22.2. These results were replicated with an affected status phenotype derived from latent class clusters. Conclusions Patterns of cosegregation of ADHD with comorbidities can inform our understanding of the inheritance patterns not only of ADHD but also of disruptive behavioral disorders and alcohol abuse/dependence. Refining the comorbid ADHD phenotype by determining the cosegregation profile of specific comorbidities might be a powerful tool for defining significant regions of linkage.