Even though there is an animal model for inattentive ADHD more work is needed before we can finish sorting out the specific genes that are involved in each subtype of ADHD. It is looking increasingly like the genes at work in inattentive ADHD are somewhat different than the genes at work in the other subtypes of ADHD. I believe that finding the specific genes involved in inattentive ADHD will give those of us with ADHD-I the validation that we need but in the mean time there has been some recent work done using personality test to predict subtype diagnosis.
Two studies just published indicate that temperament and activity level can very accurately predict the subtype diagnosis for ADHD. One study performed in Spain found that a personality inventory that measured Activity and Aggression allowed the researcher to properly classify 76 percent of individuals with inattentive ADHD.
Another study performed in England and just published in the Journal of the American Academy of Child and Adolescent Psychiatry looked at Oppositional Defiance Disorder (ODD) personality traits, temperament and activity level of preschoolers and found that increased activity and emotionality accurate predicted the diagnosis of individuals with ODD and Combined type ADHD (ADHD-C) or ADHD-HI.
We may not need a genetic marker for ADHD. It appears that personality test, which are easy to administer and readily available, are a valuable diagnostic tools currently available to make appropriate subtype distinctions in ADHD.
Journal of the American Academy of Child and Adolescent Psychiatry. 2010 May
What's in a disruptive disorder? Temperamental antecedents of oppositional defiant disorder: findings from the Avon longitudinal study.
Psicothema. 2010 May
Differential personality features in adult ADHD subtypes.
Martínez Ortega Y, Bosch Munsó R, Gomà-I-Freixanet M, Valero Ventura S, Ramos-Quiroga JA, Nogueira M, Casas Brugué M