Evaluation of ADHD typology in three contrasting samples: a latent class approach

To identify subtypes of attention-deficit/hyperactivity disorder (ADHD) and characterize them as either categorical or continuous; to investigate familial resemblance for ADHD among sibling pairs; and to test the robustness of all results by using contrasting data sets.

Latent class analysis was applied to the ADHD symptom profiles obtained from parents or best informant about their offspring in 3 samples: a population-based set of female adolescent twins (724 monozygotic pairs, 594 dizygotic pairs) and male (N = 425) and female (N = 430) child and adolescent offspring ascertained from high-risk alcoholic families.

Latent class analysis revealed 2 categories of clinically significant ADHD which were replicated in all 3 study groups: a subtype with high endorsements of ADHD inattention symptoms and a second combined type with high endorsements of both inattention and hyperactivity-impulsivity items. Both appeared to be continuous across all 3 data groups. The high-risk families contained a class in which members heavily endorsed the ADHD "fidget" item but not other ADHD items. A large proportion of the monozygotic sibs (80%) versus a smaller proportion of dizygotic sibs (52%) were assigned to the same latent class. Among the high-risk children and adolescents, 51% of the female and 41% of the male siblings were concordant for class membership.

The pattern of latent classes suggested that ADHD consists of an inattentive and a combined subtype, within each of which lies a dimensional domain. These analyses further support that genetic factors are significant determinants of latent class membership.