Replication of attention-deficit/hyperactivity (ADHD) latent class structure in a sample of Australian twins

Previous research using latent class analysis to detect ADHD subtypes based on DSM-IV symptom profiles has identified distinct, heritable phenotypes within the domains of inattention, hyperactivity-impulsivity and combined-type problems. The goal of the current research is to attempt to replicate the latent class structure in a different sample. Nine latent class models were fitted to the symptom profiles N=1432 female and N=1416 male Australian twins separately by sex. As in the Missouri sample, an 8-class solution was the best fitting model. Congruent with previous findings, substantial overlap between the DSM-IV combined subtype and severe- combined latent class membership was detected, however 60% of females and 44% of males wit no diagnosis were assigned to this class. Among DSM-IV inattentive subtypes, 84% of females and 96% of males were assigned to either the moderate or severe-inattentive classes, and the remaining cases were assigned to the moderate or severe-combined classes. 70% of individuals across all inattentive classes did not meet DSM-IV ADHD criteria. In conclusion, the latent class phenotypes only partially overlap, suggesting that the DSM nomenclature may have limited utility serving as phenotypes in genetic studies of ADHD.