Lecture psychiatric disorders 10: ADHD Flashcards
Which 3 words would you choose to describe ADHD symptoms (and are also DSM criteria)?
- Inattention
- Hyperactivity
- Impulsivity
Fill in prevalence percentages:
- …% - …% of children aged 6-16 years are diagnosed with ADHD.
- …% of all ADHD patients are boys.
- In …% - …%, symptoms will persist into adulthood.
- 2-5% of children aged 6-16 years are diagnosed with ADHD.
- 80% of all ADHD patients are boys.
- In 30% - 50%, symptoms will persist into adulthood
What’s the difference between boys and girls with ADHD?
- Boys → externalized symptoms (running and impulsivity), more physically aggressive.
- Girls → interalized symptoms (inattentiveness and low self-esteem), more verbally aggressive.
Which brain structures could be impaired in people with ADHD? Think of these brain structures and pair them with the typical ADHD symptoms.
- Prefrontal cortex → less inhibitory control and thus more impulsive.
- Cerebellum and caudate nucleus → motor hyperactivity
- Corpus callosum → less communication between hemispheres
These brain regions that have been discovered to be (thought to be) impaired in ADHD are found with neuroimaging. What is a disadvantage of these imaging studies?
Most studies are underpowered, where they used less than 20 subject per group. This makes statistics harder, which can cause differences to show up that are not really there.
The fact that most brain imaging studies for ADHD are underpowered, resulted in the generation of a meta-analysis of structural imaging findins in ADHD. What brain regions were found to be most frequently assesed as different in ADHD?
Cerebellum, corpus callosum, caudate nucleus and frontal regions.
The fact that most brain imaging studies for ADHD are underpowered, resulted in the generation of a meta-analysis of structural imaging findins in ADHD.
What’s the problem with this meta-analysis?
That there were differences between studies in experimental design.
What’s the difference between a meta- and mega-analysis?
- Meta-analysis → combining results of independent studies with different experimental designs.
- Mega-analysis → very large study with more than 1000 subjects, summarizing results of independent studies with the same experimental designs (e.g. using the same MRI data analysis)
A mega-analysis was performed where they looked at the size of different brain areas in children, adolescent and adult patients with ADHD.
What brain regions were identified for being different in ADHD patients and also name which brain regions were newly identified (i.e. not known previously to play a role in ADHD)?
- Nucleus accumbens → previously not found
- Amygdale → previously not found
- Caudate nucleus → was already known to change in ADHD patients
- Hippocampus → previously not found
- Intracranial volume → was already known
What’s interesting about identification of the nucleus accumbens (NAc) and amygdala as a brain regions that might play a role in ADHD?
- The NAc plays a role in the reward system of the brain and it might explain why ADHD patients are more likely to take risks.
- The amygdale is important for emotional regulation, it might explain why ADHD patients have difficulty with emotional regulation.
A mega-analysis was performed where they looked at the size of different brain areas in children, adolescent and adult patients with ADHD.
What did they find?
That for the whole group of ADHD patients (children, adolescents and adults) significant small changes in brain regions size were found. They saw in all patients, that there was a small significant decrease in brain size.
However, these changes were not significant for adults. It seems like the decrease in brain region size is restored in adults.
The identification of the reduction in amygdala size in ADHD patients might be important in ADHD diagnosis. Why is this?
Because emotional regulation problems often present in patients with ADHD, but this has not yet been included into the official DSM criteria.
How does this mega-analysis contribute to ADHD diagnosis?
Their finding confirm that:
- patients with ADHD have altered brains. An altered brain is seen as an disorder, so ADHD is a disorder of the brain.
- This helps reduces the stigma that ADHD is just a label for difficult children and caused by incompetent parenting.
- Better understanding of ADHD
The publishing of this mega-analysis caused criticism from other scientists. What were these criticisms, what was the reply of the author of the mega-analysis and what are the future goals of the authors?
- Criticism: only small effects are measured, it’s only on group level, it’s heterogeneous and stigmatizing.
- Reply of author: there were no claims made about causality, only claims about association of these effects to ADHD. So to make a claim about causality, we do need longitudinal studies.
- Future goals: to develop a growth curve of the brain (similar to body weight) to understand if/when children are at risk for developing ADHD.
From twin and adoption studies, there have been several behavioral traits and psychiatric disease found that have moderate/high heritability.
What is the heritability of major depression disorder (MDD), ADHD and autism, bipolar disorder and schizophrenia?
- MDD → 40-50%
- ADHD → 75%
- Autism, bipolar disorder and schizophrenia → 80%
So ADHD can be explained in part by the 75% heritability. Some weak associations have been found in two genes that can only account for about 3% of the variation in ADHD. What genes have been found?
DAT (dopamine transporter) gene and the DRD4 (dopamine receptor D4) gene
So ADHD can be explained in part by the 75% heritability. Some weak associations have been found in two genes that can only account for about 3% of the variation in ADHD.
What does this suggest?
That there are many unidentified common variants with small effects. And that gene-environment or gene-gene interactions, rare variants or a combination of these factors play a prominent role in the genetic cause of ADHD.
Are there non-genetic factors that are associated with ADHD?
Yes, since only 75% of ADHD variability can be explained by genetics/heritability, 25% should be explained by non-genetic factors.
This is indeed the case, only some non-genetic factors are only found in association with ADHD and some are probably causal.
Some non-genetic risk factors have been identified.
Name pre- and perinatal risk factors that are most likely a causal risk factor, but not yet have been proven to be causal risk factor.
Maternal smoking, alcohol and substance misuse, maternal stress and low birth weight and prematurity.