Genetic and environmental influences on adult attention deficit hyperactivity disorder symptoms: a large Swedish population-based study of twins.
BACKGROUND
Attention deficit hyperactivity disorder (ADHD) frequently persists into adulthood. Family and twin studies delineate a disorder with strong genetic influences among children and adolescents based on parent- and teacher-reported data but little is known about the genetic and environmental contribution to DSM-IV ADHD symptoms in adulthood. We therefore aimed to investigate the impact of genetic and environmental influences on the inattentive and hyperactive-impulsive symptoms of ADHD in adults.


METHODS
Twin methods were applied to self-reported assessments of ADHD symptoms from a large population-based Swedish twin study that included data from 15 198 Swedish male and female twins aged 20 to 46 years.


RESULTS
The broad heritability [i.e., A + D, where A is an additive genetic factor and D (dominance) a non-additive genetic factor] was 37% (A = 11%, D = 26%) for inattention and 38% (A = 18%, D = 20%) for hyperactivity-impulsivity. The results also indicate that 52% of the phenotypic correlation between inattention and hyperactivity-impulsivity (r = 0.43) was explained by genetic influences whereas the remaining part of the covariance was explained by non-shared environmental influences. These results were replicated across age strata.


CONCLUSIONS
Our findings of moderate broad heritability estimates are consistent with previous literature on self-rated ADHD symptoms in older children, adolescents and adults and retrospective reports of self-rated childhood ADHD by adults but differ from studies of younger children with informant ratings. Future research needs to clarify whether our data indicate a true decrease in the heritability of ADHD in adults compared to children, or whether this relates to the use of self-ratings in contrast to informant data.
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. Henrik.Larsson@ki.se
H
H
Larsson
P
P
Asherson
Z
Z
Chang
T
T
Ljung
B
B
Friedrichs
J-O
JO
Larsson
P
P
Lichtenstein
D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology / Q000209:etiology / Q000235:genetics; D004200:Diseases in Twins; D005260:Female; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease; D006801:Humans; D006948:Hyperkinesis / Q000453:epidemiology / Q000209:etiology / Q000235:genetics; D007175:Impulsive Behavior / Q000453:epidemiology / Q000209:etiology / Q000235:genetics; D008297:Male; D008875:Middle Aged; D013548:Sweden / Q000453:epidemiology; D014427:Twins / Q000235:genetics*; D055815:Young Adult