Familial clustering of symptoms and disruptive behaviors in multiplex families with attention-deficit/hyperactivity disorder

Objective: To examine familial clustering of attention-deficit/hyperactivit y disorder (ADHD), ADHD subtypes, symptoms, and oppositional behaviors in a ffected sibling pairs (ASPs) and their parents. Method: One hundred thirty- two ASPs, ranging in age from 5 to 25 years and ascertained through clinic and volunteer referrals, were examined for DSM-IV ADHD subtypes, opposition al defiant disorder (ODD), and conduct disorder (CD) with the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and L ifetime version (K-SADS-PL). Two hundred fifty-six parents in these familie s were assessed by means of the SADS-Lifetime version, Modified for the Stu dy of Anxiety Disorders, Updated for DSM-IV(SADS-LA-IV), and the Behavioral Disorders supplement of the K-SADS-PL to determine ADHD, ODD, and CD. Resu lts: Fifty-five percent of families ascertained through an ASP have at leas t one parent with a lifetime diagnosis of ADHD. The frequency of ADHD in at least one parent was higher in families with at least one affected girl (6 3%) than in families with only affected boys (45%) (p= .02). There was no e vidence that affected siblings or parents within ASP families showed simila r patterns of ADHD symptoms, such as ADHD subtype classification. In contra st, CD significantly clustered in ASP families. Conclusions: The sex differ ence in prevalence of ADHD among ASPs is consistent with a model of inherit ance in which girls require a greater loading of familial influences to dev elop ADHD. The lack of familial clustering of ADHD symptoms within ASP fami lies suggests that hyperactive and inattentive symptoms reflect common fami lial underpinnings and not unique familial effects. in contrast, CD seems t o reflect unique familial underpinnings distinct from those underlying ADHD .