1. TODAY…. TOMORROW…. trials and errors diagnosis effective treatment
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2. Pharmacogenetics Hypothesis Advantages
Variability in response, toxicity and adverse effects following drug treatment is influenced by genetic variation
Advantages
Genotyping can be done any time
Not influenced by current treatment
Can be measured very reliably
Genome fully sequenced
Easy to do – peripheral blood sample

3. Heritability – a starting point
FHx of response or side effects
Poor man’s pharmacogenetics?
Antidepressants
38 family pairs concordant for response to Imipramine (Angst, 1964)
12/12 and 10/12 concordance of first degree relatives (Pare et al. 1962; Pare & Mack, 1971)
Retrospective study in 4 families who responded to tranylcypromine but not other ADs (O’Reilly et al. 1994)
67% of 1° rels of fluvoxamine responders responded (Franchini et al. 1998)
Antipsychotics
Afro-Caribbean greater acute response than Caucasians (Emsley et al. 2002)
Little other supportive data

4. Definition of some terms
Pharmacogenetics
The study of candidate genes that may influence drug effects and metabolism
Pharmacogenomics
The study of all genes (and their expression) in the genome that may influence drug effects and metabolism
Non-hypothesis based
Needs large-scale high-through put techniques to screen the genome

5. Genetic Variation Polymorphism
Genetic variation that occurs with a frequency ≥ 1% in the population
Various types
SNPs (Single nucleotide polymorphisms)
Repetitive DNA sequences
Must be functional (?)
Alter the expression levels or conformation of a drug-related protein

6. Single Nucleotide Polymorphism (SNP) in the Coding Region of a Gene
SNP results in alteration of the amino acid sequence of the corresponding protein
arginine (Arg) substituted for glycine (Gly)
Distinct protein structures could result in phenotypic differences between the subjects, such as variation in response to medication.
Taken from Malhotra et al Am.J.Psych.

7. Absorption/ Excretion
Pharmacogenetic tree
Absorption/ Excretion
Pharmacokinetics
study of availability of therapeutic in body
CYP450:
76% of ADRs are dose dependent
CYP450 is one of the best characterized metabolic protein complexes
Metabolism
Distribution
Pharmacogenetics
study of correlation between genetic traits and response to therapeutics (efficacy and adverse effects)
Receptors
The internal communications team:
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Pharmacodynamics
study of drug and target interaction
Pharmacodynamics
Study of drug and
target interactions
Transporters/Channels
Enzymes

8. CYP 450 and metabolism of TCAs
Marked genetic variation in hepatic metabolism
Up to 30-fold variation in plasma concentrations between individuals
N.B. cardiac arrhythmias occur at concentrations just 10-fold higher than monoamine uptake blockade
Main rate limiting step in TCA metabolism is mediated by CYP2D6 isoenzyme
7% of Caucasians have a functional impairment of this enzyme which can lead to toxic levels occurring

9. Drug Concentrations by Genotype
Metabolizer Status
Genotype
Response to average daily dose
Ultrarapid
Conc.
Time
Extensive
normal activity
reduced activity
= Adverse Events
= Therapeutic Window
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Intermediate
no activity
Poor

10. Ingelman-Sundberg (2001) Journal of Internal Medicine 250: 186
Regional distribution of ultrarapid metabolisers
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Ingelman-Sundberg (2001) Journal of Internal Medicine 250: 186

11. CYP2D6 and dosing of antidepressants
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Source: Kirchheiner et al., Mol Psychiatry 9:

12. CYP2D6 and dosing of antipsychotics
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Source: Kirchheiner et al., Mol Psychiatry 9:

14. CYP450 Polymorphism Findings
No confirmed association between CYP450 polymorphisms and response to antipsychotics or antidepressants identified to date (see Vetti et al. 2010)
CYP2D6 and CYP1A2 associated with increased side effects of antipsychotics (TD and PSx)(Basile et al. 2000; Lam et al. 2001)
CYP2D6 and CYP2C19 associated with increased side effects with sertraline (Wang et al. 2001)
N.B. wide therapeutic index with SSRIs

15. P-glycoproteins and antidepressant response
P-glucoproteins (P-gp) are transport proteins that occur around the body, including in the BBB
Includes the MDR1 (ABCBB1) protein
Can influence the entry of drugs into the brain

16. Organ/plasma ration of antidepressants in ABCB1 mutant mice
Uhr, M. et al Neuron 57:

17. P-gp polymorphisms and response to antidepressants
362 patients treated with P-gp substrates (amitriptyline, citalopram, paroxetine, venlafaxine) or non-substrate (mirtazepine)
9.5% non-remitters carried C allele vs 45% of remitters
C-carriers treated with P-gp substrate significant increased risk of remission
Uhr, M. et al Neuron 57:

19. Pharmacodynamics The interaction of a drug with a target molecule
Receptors, enzymes, transporters, ion channels
Leads to therapeutic effects
Can lead to side effects

20. 5-HTT/SERT 5HTTLPR polymorphism
Serotonin transport gene polymorphisms
The brain serotonin transporter (5HTT) is the principal site of action of many antidepressants.1
Transcriptional activity of the 5HTT gene is modulated by a gene linked polymorphic region (5HTTLPR).2
The short (s) allele is associated with lower transcriptional efficiency than the long (l) allele.2
Serretti A et al. Prog Neuro Psychopharmacol Biol Psychiatry 2005;29:
Lesch KP et al. Science 1996 ;274:
Diagram from Canli T & Lesch KP. Nat Neurosci 2007;10:

21. Genetic (5-HTTLPR polymorphism) influence on response to stress
Trier Social Stress Test in healthy subjects2
Association of stressful life events aged 21-26yrs and depression outcome aged 26 as a function of 5HTT geneotype.1
Meta analysis demonstrates greater amygdala activity in s allele carriers when shown pictures of fearful faces.3
Caspi A et al. Science 2003; 301: Way BM & Taylor SE. Biol Psychiatry 2010;67:
3. Munafo MR et al. Biol Psychiatry 2008;63:

22. SSRIs and 5-HTT/SERT (from Schosser & Kasper, 2009)

26. 5-HTTLPR effects may be mediated via complex and indirect effects

27. 5-HT Receptors and antidepressants
5-HT1A polymorphism
Functional
Associated with alterations in expression of 5-HT1A receptors (Lemonde et al. 2003)
Associated with response to TCAs and SSRIs (Serretti et al. 2004; Lemonde et al. 2004)
5-HT2A polymorphism
Association found in largest pharmacogenetics study (n = 1953, 768 SNPs examined)
79.9% vs 62.4% response rates for homozygous patients (McMahon et al. 2006)

28. Antidepressants and other polymorphisms
Glutamate receptor polymorphism associated with response to citalopram (Paddock et al. 2007)
GRIK4
Glutamate receptor polymorphism associated with treatment emergent suicidal ideation with citalopram (Laje et al. 2007; Menke et al. 2008)
GRIK2 (kainate-sensitive ionotropic glut receptor – GluR6)
GRIA3 (ionotropic glut receptor – AMPA3)
CREB1 (cAMP response element binding protein 1) associated with treatment emergent suicidality in men (Perlis et al. 2007)
NET polymorphisms and response to nortriptyline Uher et al. 2009)
GR polymorphisms associated with response to escitalopram and nortriptyline (Uher et al. 2009)

29. GWAS and antidepressants
Three independent samples have so far been studied using GWAS1:
Sequenced Treatment Alternatives to Relieve Depression sample (STAR*D) (n=1953)
Munich Antidepressant Response Signature (MARS) sample (n=339)
Genome-based Therapeutic Drugs for Depression (GENDEP) sample (n=706).
None reported results that achieved genome-wide significance
Larger samples and better outcome measures are needed.
1 – Laje & McMahon, 2011 Prog Neuropsychopharm Biol Psychiatry 15:1553-7

30. CLOCK gene – multiple effects
CLOCK 3111T/C Polymorphism
Associated with “eveningness” (healthy subjects)
Associated with a higher recurrence of episodes (BP)
Associated with lifetime insomnia (BP+UP)

32. CLOCK gene variants and insomnia during SSRI treatment
p=0.0443
p=0.0379
p=0.0195
p=0.0050
HAMD insomnia score
Weeks of treatment

34. Zang & Malhotra (2011) - summary
Most pharmacogenetic studies of antipsychotic drugs have used a candidate gene approach, focusing on polymorphisms in genes coding for receptors in the dopamine and 5-HT systems, as well as genes coding for enzymes that metabolize drugs, such as COMT and CYP2D6.

35. Zang & Malhotra (2011) - summary
Regarding genetic variants predicting antipsychotic drug efficacy, previous studies have produced promising results for a few polymorphisms including the -141C Ins/Del in DRD2, Ser9Gly in DRD3, -1438G/A in HTR2A, 5-HTTLPR and Val108Met in COMT.
Studies with larger samples and better designs are needed to validate these findings.

36. Zang & Malhotra (2011) - summary
Regarding genetic variants predicting antipsychotic-induced side effects, different studies have been inconsistent.
For tardive dyskinesia, the Taq1A in DRD2, the Ser9Gly in DRD3, the T102C SNP (single nucleotide polymorphism) in HTR2A and the loss of functional variants in CYP2D6 may warrant further research.

37. Replicated data for leptin and 5-HT2C genes Also evidence for:
Pharmacogenetics of antipsychotic induced weight gain (Lett et al Mol Psychiatry)
Replicated data for leptin and 5-HT2C genes
Also evidence for:
DRD2, TNF, SNAP-25 and MC4R genes
Preliminary evidence for:
CNR1, MDR1, ADRA1A and INSIG2

38. Combinations of genes
Combining information from key response-related genes
Can constantly refine predictions by adding additional genes
Will need adjustments for ethnic mix
Examples:
DRD3 and 5-HT2C polymorphisms have additive effects on risk of TD (Segman & Lerer 2002)
DRD3 and CYP1A2 polymorphisms additive effects on risk of TD (Basile et al. 2000)
Response in Alzheimers predicted by combination of polymorphisms of APOE, PS1 and PS2 (Cacabelos et al. 2000)
Problems
What statistical methods should be used?
Effects additive or synergistic?

39. Genes investigated in the short term response to antidepressants
5-HTTLPR
SERT-STin2
5HT1A C-1019G
5-HT1B
5HT2A T102C
5HT2A G1438A
5HT2C
5HT6 C267T
TPH1 A218C TPH2
NET T-182C
COMT
MAOA
DRD2 S311C
DRD4 VNTR
ACE I/D polymorphism
G-protein beta3 C825T
ADRB1 G1165C
CRHR1
NOS C276T
IL-1beta C511T
CRHR1
DTNBP1
FKBP5
CLOCK
BDNF
nNOS
IL-1beta
APOE
MDR1P-gp
A-161T
Dysbindin

40. Genes investigated in the short term response to antidepressants
5-HTTLPR
SERT-STin2
5HT1A C-1019G
5-HT1B
5HT2A T102C
5HT2A G1438A
5HT2C
5HT6 C267T
TPH1 A218C TPH2
NET T-182C
COMT
MAOA
DRD2 S311C
DRD4 VNTR
ACE I/D polymorphism
G-protein beta3 C825T
ADRB1 G1165C
CRHR1
NOS C276T
IL-1beta C511T
CRHR1
DTNBP1
FKBP5
CLOCK
BDNF
nNOS
IL-1beta
APOE
MDR1P-gp
A-161T
Dysbindin

43. Number of episodes
Side effects (yes/no)
Delusional features (yes/no)
Baseline HAM-D
Length of current episode
Lithium augmentation (yes/no)
Current medical condition (y/n)
Personality disorders (yes/no)
Sex (female/male)
Age at onset
Polarity (UP/BP)
Plasma level
Baseline VAS
HAMD
improvement

44. 21% Variance explained Number of episodes Side effects (yes/no)
Delusional features (yes/no)
Baseline HAM-D
Length of current episode
Lithium augmentation (yes/no)
Current medical condition (y/n)
Personality disorders (yes/no)
Sex (female/male)
Age at onset
Polarity (UP/BP)
Plasma level
Baseline VAS
HAMD
improvement
21% Variance
explained

45. Genes investigated in the short term response to antidepressants
5-HTTLPR
SERT-STin2
5HT1A C-1019G
5-HT1B
5HT2A T102C
5HT2A G1438A
5HT2C
5HT6 C267T
TPH1 A218C TPH2
NET T-182C
COMT
MAOA
DRD2 S311C
DRD4 VNTR
ACE I/D polymorphism
G-protein beta3 C825T
ADRB1 G1165C
CRHR1
NOS C276T
IL-1beta C511T
CRHR1
DTNBP1
FKBP5
CLOCK
BDNF
nNOS
IL-1beta
APOE
MDR1P-gp
A-161T
Dysbindin

46. Prediction of Clozapine response (Arranz et al. 2000)
200 schizophrenia patients (all white Caucasians of British origin) treated with clozapine (133 responded)
19 polymorphisms analysed
6 with strongest association with response (5-HT2A X 2, 5-HT2C X 2, 5-HTT, H2) combined
PPV: 0.76 ± 0.08
NPV: 0.82 ± 0.16
Sensitivity 95.9% ± 0.04% (for identifying “satisfactory” responders)
Specificity 38.3 % ± 0.14% (for identifying poor responders)
Utility?

47. N.B. Ethical, Legal and Social Implications
Use of genetic information by insurers, employers...
Who should have access to personal genetic information, and how will it be used?
Privacy and confidentiality.
Who owns and controls genetic information?
Stigmatization.
How does personal genetic information affect an individual and society's perceptions of that individual?
More information at

49. Pharmacogenetics Conclusions
Pharmacogenetics: Any relevance to clinical practice?
Possibly….
CYP450 chip technology may be helpful for a minority of patients
Use of pharmacogenetics for efficacy predictions (e.g. for clozapine) less clear
The future (5-10 years) does potentially look very interesting