Review: changing (shared) heritability of ASD and ADHD across the lifespan

Excerpt

Autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) frequently co-occur. In clinical practice, we daily struggle deciding if one, or the other, or both disorders, best describe the child’s problems. A strong body of literature has convincingly shown that large overlap exists regarding genetic factors [6, 11, 26, 29]. However, this genetic overlap may significantly depend on age. It is well known that genetic influences on behavior are not at all constant during development and continuously co-act and interact with environmental factors influencing behavioral functioning [1, 30]. For example, increasing heritability can result from amplification, whereby early genetic influences become stronger across time. As a second example, genetic influences may be stable; yet novel genetic influences may emerge with time while early genetic influences may decrease [2]. Despite everyone’s awareness of change in the (genetic) mechanisms underlying the development of an individual until elderly age in typical development, studies on neurodevelopmental disorders like ADHD and ASD have been strongly focused on childhood. The age of onset for ASD and ADHD is nearly always in childhood ([18]; but see [17]), which is the likely reason for this bias. However, given that it is already well known that developmental changes take place in both ADHD and ASD symptom domains separately, a focus beyond childhood is needed to further understand the potentially changing etiology of ADHD–ASD co-occurrence. …