Scientific Update of ADHD Russell Schachar The Hospital for Sick
Children Department of Psychiatry Brain and Behaviour Programme
University of Toronto Slide 2 Affiliations CIHR CIHR Barr, Kennedy,
Ickowicz, Crosbie, Pakulak, Ornstein Barr, Kennedy, Ickowicz,
Crosbie, Pakulak, Ornstein Noseworthy, Chevrier Noseworthy,
Chevrier Robaey, Perusse Robaey, Perusse NINDS NINDS Levin, Dennis,
Barnes Levin, Dennis, Barnes Lilly Lilly Purdue Frederick Purdue
Frederick Shire Shire Slide 3 Outline Summary and overview current
understanding Summary and overview current understanding
Neuroscience 101 Neuroscience 101GenesProteins Brain structure
Cognitive function Behavior Caveats Caveats Slide 4 g 1 g 2 g 3
Cell membranes, transmitters, assemblies Proteins function
hyp-impinattention ADHD environment Slide 5 Genetics Slide 6 What
are genes? DNA is specific sequence of nucleotide bases that encode
instructions for proteins DNA is specific sequence of nucleotide
bases that encode instructions for proteins Genome is complete set
of DNA Genome is complete set of DNA Slide 7 How do genes function?
Many changes evident and passed on Most changes cannot be seen by
microscope Most base pairs are not involved in genes and are not
functional Can be used to track functional changes May regulate
gene expression or function Epigenetic factors affect gene function
Many hereditary effects may be outside of genes Slide 8
Neurotransmitter systems Dopamine transporter Serotonin
Noradrenalin Glutamate GABA Transporters and receptors variably
distributed Slide 9 Dopamine D4 48bp Repeat Variants: Pharmacologic
differences not linearly correlated with number of repeats EC 50
2R4R 7R10R Asghari et al, 1995 Jovanovic et al, 1999 Implication:
the 7R allele has a blunted response to dopamine Slide 10 SNAP-25
Critical for controlled release of neurotransmitters into the
synaptic cleft Loss of expression of a single copy of the gene
results in dysregulation in the controlled release of glutamate,
dopamine, and serotonin in select brain regions SNAP-25 Slide 11
Genes, proteins and neural development Slide 12 Neural development
Stem cells differentiate Stem cells differentiate Growth factors
(sonic hedgehog, notch, BDNF) Growth factors (sonic hedgehog,
notch, BDNF) Half survive Half survive Development depends of where
they end up, activity there (use it or lose it!) Development
depends of where they end up, activity there (use it or lose it!)
Rate of division/survival depends on experience, formation of
synapses, integration into networks Rate of division/survival
depends on experience, formation of synapses, integration into
networks Loss of neurons normal (exaggerated in some diseases) Loss
of neurons normal (exaggerated in some diseases) Neurons likely
regenerate and affected by experience (can teach old dog new
tricks) Neurons likely regenerate and affected by experience (can
teach old dog new tricks) Environment can affect gene expression
Environment can affect gene expression Slide 13 Brain tour Slide 14
Phineas Gage Slide 15 Prefrontal cortex Not involved in specific
tasks Not involved in specific tasks Executive control of
behaviour, thought and affect Executive control of behaviour,
thought and affect Organization and planning for future action and
social goals Organization and planning for future action and social
goals Balances perceptual, instinctual and motivational input
Balances perceptual, instinctual and motivational input Reflective:
guided by internal states and intentions Reflective: guided by
internal states and intentions Control subordinate attention and
motor processes Control subordinate attention and motor processes
Slide 16 Prefrontal subcortical circuits Begin and end in frontal
cortex Begin and end in frontal cortex Pass through subcortical
structures Pass through subcortical structures Reciprocal and
interacting connections Reciprocal and interacting connections
Excitatory and inhibitory neurotransmitters Excitatory and
inhibitory neurotransmitters Separate yet overlapping and
interacting Separate yet overlapping and interacting Specific and
intermingled mixture of deficits Specific and intermingled mixture
of deficits Evident in individuals with massive lesions Evident in
individuals with massive lesions Slide 17 Dorsolateral circuit
Organization, planning, attention Organization, planning, attention
Lesions generate concrete thinking, inability to stop, shift set,
filter and ignore distractions, plan and organize Lesions generate
concrete thinking, inability to stop, shift set, filter and ignore
distractions, plan and organize Slide 18 Orbitofrontal circuit
Mediates socially appropriate behaviour Mediates socially
appropriate behaviour Lesions lead to marked personality change,
social disinhibition, explosiveness, tactlessness, lability, lack
of interpersonal sensitivity Lesions lead to marked personality
change, social disinhibition, explosiveness, tactlessness,
lability, lack of interpersonal sensitivity Slide 19 Anterior
cingulate circuit Motivation, balancing competing demands,
performance monitoring Motivation, balancing competing demands,
performance monitoring Lesions result in akinetic mutism, apathy,
lack of motivation, insensitive to errors Lesions result in
akinetic mutism, apathy, lack of motivation, insensitive to errors
Slide 20 Frontal/ executive processes wave of attention Encoding,
maintaining, retrieving in working memory Encoding, maintaining,
retrieving in working memory Preparing and anticipating Preparing
and anticipating Interference management Interference management
Withholding of response tendency Withholding of response tendency
Maintain set Maintain set Retract or inhibition Retract or
inhibition Error detection Error detection Error correction Error
correction Slide 21 Summary Considerable understanding of brain
development and function Considerable understanding of brain
development and function Differentiation in structure and function
Differentiation in structure and function Cognitive deficits
Cognitive deficits Genetic risks Genetic risks Structural and
functional anomalies Structural and functional anomalies Slide 22
ADHD genetics Highly genetic Highly genetic Not simple Mendelian
inheritance Not simple Mendelian inheritance Multigenic Multigenic
Non-genetic factors contribute separately and through various
combinations Non-genetic factors contribute separately and through
various combinations Disorder occurs when combination of genetic
and non-genetic factors exceeds some threshold Disorder occurs when
combination of genetic and non-genetic factors exceeds some
threshold Nature of risk and mode of inheritance unknown Nature of
risk and mode of inheritance unknown Slide 23 Genetics of ADHD %
risk to family% concordance Slide 24
D19S229D19S247D19S204D19S221D19S179D19S248D19S178D19S246D19S180D19S254
Genome Scan Systematically screen all of the chromosomes for
linkage using DNA markers spaced at regular intervals Slide 25
Genome scans for ADHD Fisher et al., 2002 Fisher et al., 2002 UCLA
126 affected sib pairs UCLA 126 affected sib pairs no regions met
genome-wide significance levels no regions met genome-wide
significance levels suggestive 5p12, 10q26, 12q23, 16p13 (Smalley,
2002) suggestive 5p12, 10q26, 12q23, 16p13 (Smalley, 2002) Ogdie et
al., 2003 Ogdie et al., 2003 expansion of Fisher et al., sample +
144 sib pairs expansion of Fisher et al., sample + 144 sib pairs
17p11 (LOD 2.98), 16p13 17p11 (LOD 2.98), 16p13 Bakker et al., 2003
Bakker et al., 2003 164 Dutch affected sib pairs 164 Dutch affected
sib pairs regions with LOD scores > 3, 15q15.1, 7p13 regions
with LOD scores > 3, 15q15.1, 7p13 LOD score > 2, 9q33.3 LOD
score > 2, 9q33.3 Slide 26 Candidate gene study Case-control
Case-control Compare samples Compare samples Ethnicity Ethnicity
Associated characteristic or disorder Associated characteristic or
disorder Family-based Family-based Compare children and their
parents or siblings Compare children and their parents or siblings
Slide 27 Dopamine, cognition and behaviour Neurotoxin reduces DA in
rats Neurotoxin reduces DA in rats hyperlocomotion, learning
problems hyperlocomotion, learning problems DA depletion impairs
working memory DA depletion impairs working memory Impulsiveness
associated with low extracellular DA Impulsiveness associated with
low extracellular DA Blocking DA reuptake makes DA more available
and improves executive control Blocking DA reuptake makes DA more
available and improves executive control Slide 28 Drugs and ADHD
Slide 29 54 75 % adults and children with ADHD responds to
methylphenidate (0.6 mg/kg) (Spencer et al 2001) The behavioural
modifications induced by stimulants occurs with the reaching of
peak plasma level Psychostimulants and ADHD Slide 30 Dopamine
Transporter Some individuals with ADHD, have higher expression of
the dopamine transporter. Some individuals with ADHD, have higher
expression of the dopamine transporter. Possible mechanism of
genetic susceptibility is over expression of the DAT protein
Possible mechanism of genetic susceptibility is over expression of
the DAT protein Stimulants blockade dopamine transporter and
temporarily correct the levels of dopamine. Stimulants blockade
dopamine transporter and temporarily correct the levels of
dopamine. DAT Knock Out mouse DAT Knock Out mouse difficulty
shifting - perseverative errors difficulty shifting - perseverative
errors novelty-driven hyperactivity novelty-driven hyperactivity
spatial learning deficit spatial learning deficit Slide 31 1)
hyperactive 2) responsive to dextroamphetamine 3) not responsive to
methylphenidate 4) delayed in some developmental milestones
Rationale: mouse irradiation mutant strain Coloboma has a single
copy of the SNAP-25 gene. The other copy has been deleted.
Synaptosomal-Associated Protein of 25 kDa (SNAP-25) Slide 32 A
number of Genes Identified as linked to ADHD What now? Confirm
linkage in larger samples Determine how these genes contribute to
ADHD Additional candidates e.g., neurotrophic factors Slide 33
Neuroimaging Computed tomography (CT) Series of x rays from
different angles Positron emission tomography (PET) Inject
radioisotope that emits positrons Water labelled with oxygen-15
measure changes in blood flow Deoxyglucose labelled with florine-18
which accumulates in active cells Magnetic resonance imaging (MRI)
Magnets detect magnetic molecules fMRI detects changes in magnetic
properties of hemoglobin as it carries O 2 to active brain cells
Slide 34 Slide 35 Brain structure and ADHD Slide 36 Inhibitory
control Withholding and withdrawing of responses if intention or
circumstances change or error is made Withholding and withdrawing
of responses if intention or circumstances change or error is made
Failure of inhibition results in errors & impulsiveness Failure
of inhibition results in errors & impulsiveness Slide 37
Inhibition and ADHD Activates orbital, DLPF and basal ganglia
Activates orbital, DLPF and basal ganglia Rich in DA Rich in DA
Disruption of DA by knock out or neurotoxins affects executive
control Disruption of DA by knock out or neurotoxins affects
executive control DA tone associated with executive control DA tone
associated with executive control Impulsiveness associated with low
extracellular DA Impulsiveness associated with low extracellular DA
Blocking DA (mostly in basal ganglia) reuptake makes DA more
available and improves executive control Blocking DA (mostly in
basal ganglia) reuptake makes DA more available and improves
executive control Slide 38 500 ms 1000 ms Inter-trial interval =
3000 ms Stop Signal Task motor response * X/O fixation point go
stimulus: choice reaction time task Slide 39 * X/O 500 ms 1000 ms
Stop Signal Task stop signal delay (variable) RED SCREEN or TONE
500 ms stop signal Slide 40 Latency of inhibition (SSRT) in ADHD
and controls SSRT (ms) Schachar et al., 2001 Slide 41 Inhibition
& psychopathology Osterlaans et al., 1999 IQ, age, aggression,
speed, reading Slide 42 Impulsive Personality Slide 43 Inhibition
and Methylphenidate Response Tannock, Schachar & Logan, 1995
T-score (Mean = 50, SD = 10) Slide 44 Slide 45 Inhibition in
concordant and discordant siblings ConcordantDisconcordantControls
SSRT ms Slide 46 Evidence of performance monitoring Introspection
Introspection Slowing following errors Slowing following errors
Slowing following correct responses Slowing following correct
responses Self-detected action slips or errors due to faulty
knowledge (external feedback) Self-detected action slips or errors
due to faulty knowledge (external feedback) Pattern seen in range
of tasks Pattern seen in range of tasks Speeded choice response
tasks Speeded choice response tasks Memory tasks Memory tasks
Inhibition tasks Inhibition tasks Slide 47 Relevance of performance
monitoring to ADHD Poorly regulated behaviour Poorly regulated
behaviour often fails to give close attention to details or makes
careless mistakes in schoolwork, work, or other activities often
fails to give close attention to details or makes careless mistakes
in schoolwork, work, or other activities Inaccurate and variable
task performance Inaccurate and variable task performance Slide 48
Slowing after non-stopped responses in ADHD and controls ms Slide
49 Executive control summary New breed of measures of specific
processes New breed of measures of specific processes Cognitively
and neurally distinct, multiple deficits characteristic of ADHD
Cognitively and neurally distinct, multiple deficits characteristic
of ADHD Functional assessment warranted Functional assessment
warranted Slide 50 What do you mean Cognitive tests are not
diagnostic? Clinic sample (N = 100) Clinic sample (N = 100)
ADHDcontrols 50/2550/5 Of 30 cases with diagnostic marker, 25/30
=83% will be ADHD General population (N = 100) General population
(N = 100) ADHDcontrols 5/2.595/19 Therefore, of every 21.5 cases
with the diagnostic marker, 19/21.5 = 88% will be controls! Slide
51 Environmental causes of ADHD/cognitive deficit Traumatic
Traumatic closed head injury closed head injury prematurity
prematurity radiation radiation Toxic Toxic alcohol (FAS) alcohol
(FAS) smoking smoking Social / stress (alteration in DA, NA, S
release in PFC) Social / stress (alteration in DA, NA, S release in
PFC) in animals & humans disrupts complex cognitive function in
animals & humans disrupts complex cognitive function maternal
stress during pregnancy maternal stress during pregnancy disrupted
early caregiving disrupted early caregiving Slide 52 School policy
dilemma ADHD is a learning problem associated with cognitive
deficits and academic underachievement ADHD is a learning problem
associated with cognitive deficits and academic underachievement
Slide 53 Approach differs from RD But is handled differently than
learning disability Accommodation in classroom Slide 54 Summary
Heritable Heritable Genetic risks Genetic risks Structure Structure
Function Function Non-genetic factors Non-genetic factors
Educational system Educational system Slide 55 Opportunities for
participation Children 6 -16 years Children 6 -16 years Presumptive
diagnosis of ADHD Presumptive diagnosis of ADHD Two affected
children and both parents Two affected children and both parents
Willing to give blood Willing to give blood No exclusions No
exclusions Teju Pathare(416) 813-8291 Teju Pathare(416) 813-8291
One affect, sibling unaffected One affect, sibling unaffected
Tracee Francis(416) 813-6568 Tracee Francis(416) 813-6568