2. Determine the sequence of the 3 billion nucleotides that
make up human DNA
Characterize variability in the genome
Identify all the genes in human DNA
The Era of Genomic Medicine:
Improve prediction of drug efficacy or toxicity
Improve the diagnosis of disease
Earlier detection of genetic predisposition to disease
3. DNA
A, T, G, C
Codon
Gene
Chromosome
Genome
ENGLISH
Abcdefg….xyz
Word
Sentence
Chapter
Book
5. Age
Race/ethnicity
Weight
Gender
Concomitant Diseases
Concomitant Drugs
Social factors
GENETICS
PERSONALIZED
MEDICINE
6. Pharmacogenetics
Study of how genetic differences in a SINGLE
gene influence variability in drug response (i.e.,
efficacy and toxicity)
Pharmacogenomics
Study of how genetic (genome) differences in
MULTIPLE genes influence variability in drug
response (i.e., efficacy and toxicity)
7. Hypothesis
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
9. Maximize drug efficacy
Minimize drug toxicity
Predict patients who will respond to intervention
Aid in new drug development
10. Mutation: difference in the DNA code that
occurs in less than 1% of population
Often associated with rare diseases
Cystic fibrosis, sickle cell anemia, Huntington’s
disease
Polymorphism: difference in the DNA code
that occurs in more than 1% of the population
A single polymorphism is less likely to be the
main cause of a disease
Polymorphisms often have no visible clinical
impact
11. Pronounced “snip”
Single base pair difference in the DNA sequence
Over 2 million SNPs in the human genome
Other polymorphisms:
Insertion/deletion polymorphisms
Gene duplications
Gene deletions
12. Alleles = different DNA
sequences at a locus
Codon 389 1-AR
Arg (0.75)
Gly (0.25)
Genotype = pair of alleles a
person has at a region of the
chromosome
Codon 389 1-AR
Arg389Arg
Arg389Gly
Gly389Gly
14. Evidence of an inherited basis for drug response
dates back in the literature to the 1950s
Succinylcholine: 1 in 3000 patients developed
prolonged muscle relaxation
Monogenic
Phenotype to genotype approach
15. CYP2D6 is responsible for the metabolism of a number of different
drugs
Antidepressants, antipsychotics, analgesics, cardiovascular drugs
Over 100 polymorphisms in CYP2D6 have been identified
Based on these polymorphisms, patients are phenotypically
classified as:
Ultrarapid metabolizers (UMs)
Extensive metabolizers (EMs)
Poor metabolizers (PMs)
16. Increased rate of adverse effects in poor metabolizers due to
increased plasma concentrations of drug:
Fluoxetine (Prozac) death in child attributed to CYP2D6 poor
metabolizer genotype
Side effects of antipsychotic drugs occur more frequently in
CYP2D6 poor metabolizers
CYP2D6 poor metabolizers with severe mental illness had more
adverse drug reactions, increased cost of care, and longer hospital
stays
17. Treatment of attention deficit hyperactivity disorder
CYP2D6 poor metabolizers have 10-fold higher
plasma concentrations to a given dose of
STRATTERA compared with extensive metabolizers
Approximately 7% of Caucasians are poor
metabolizers
Higher blood levels in poor metabolizers may lead to
a higher rate of some adverse effects of STRATTERA
18.
19. The Roche AmpliChip CYP450 Test is intended to identify a patient's
CYP2D6 and CYP2C19 genotype from genomic DNA extracted from a
whole blood sample.
Information about CYP2D6 and CYP2C19 genotype may be used
as an aid to clinicians in determining therapeutic strategy and treatment
dose for therapeutics that are metabolized by the CYP2D6 or CYP2C19
gene product.
20.
21. Direct protein target of drug
Receptor
Enzyme
Proteins involved in pharmacologic response
Signal transduction proteins or downstream proteins
Polymorphisms associated with
disease risk
“Disease-modifying” polymorphisms
“Treatment-modifying” polymorphisms
POLYGENIC
22.
23. Depression—Symptom rating scales
Indirect measure of drug response
Inter-rater reliability
Hypertension—Blood pressure
Minute to minute and diurnal variability
Influence of environmental factors (e.g. lack of rest before
measurement)
Diabetes—Blood glucose
Diurnal variation in blood glucose
Influence of environmental factors (e.g. diet/exercise)
24. It required a shift in clinician attitude and beliefs “not one
dose fits all”
Paucity of studies demonstrating improved clinical benefit from
use of pharmacogenomic data
Still much to be learned
Even some of the black block warnings currently on
drug labels may be overcalls of importance
Genome wide interrogation will likely be important to get the
entire picture
25. Larry Lesko, Director of the FDA Office of Clinical
Pharmacology and Biopharmaceutics
26.
27. Despite the enormous progress made in the understanding of
the neurobiology of MDD, treatment outcomes have improved
only slightly in the past few decades in spite of the broadening
of the target spectrum of antidepressants (ADs).
The recent Sequence Treatment Alternatives to Relieve
Depression (STAR*D) study indicate that even with systematic
measurement-based treatment, only approximately 50% of
patients show response to treatment after one treatment trial,
and only 30% of patients reach full remission.
28. There is a significant decrease in remission rate after two
failed trials, with only 60% reaching full remission after
four treatment trials
The long duration required to conclude treatment success
or failure (eight to twelve weeks) can prove to be a
difficult and frustrating experience for the patient and the
family and may even increase the risk of suicide,
29. Besides failure to reach remission, relapse rate is
also over 40%, especially in patients who did not
achieve full remission.
Treatment resistant depression (TRD) is an
extremely common problem, affecting a large
proportion of all patients suffering from major
depressive episodes
30. Since genetic factors contribute for about 50% of the
Adverse response, pharmacogenetic researchers have
assumed that in order to minimize disorder duration
and re-duce the occurrence of Adverse response it
would be useful to be able to predict the
pharmacological intervention likely to be effective and
tolerable for each patient according to the patient’s
specific genetic makeup.
31.
32. The cytochrome P450s (CYPs) are members of a
superfamily of oxidative enzymes, and act as the major
system for phase I oxidative metabolism of approximately
80% of the commonly used therapeu-tic substances
This important endogenous system has received the most
attention by pharmacogenetic researchers, leading to the
discovery of 58 different human CYP genes with various
polymorphisms that affect drug metabolism
33. The variations of DNA within the coding genes may
contribute to excessive metabolism as well as diminished
or absent metabolism of a drug, leading to the prolonged
presence of a toxic dose or failure to reach therapeutic
dose of the given medication.
The clinically most important isoenzymes of he-patic
CYPs, regarding AD metabolism, are CYP1A2, CYPC9/19,
CYP2D6, CYP3A4 and CYP2B6
34. The majority of ADs (fluoxetine; fluvoxamine; paroxetine;
venlafaxine; mirtazapine; amitriptyline; imipramine;
trimipramine; desipramine; nortriptyline) are metabolized
primarily by CYP2D6
35. CYP2D6 is the most researched gene in the field of
pharmacogenetics, and more than 100 different alleles
were identified which determine the level of activity of the
enzyme
According to the number of gene copies inherited,
individuals are classified as :
poor (PM),
intermediate (IM),
extensive (EM), or
ultrarapid metabolizers (UM).
36. A gene x environment effect has been shown
concerning the CYP1A2 izoenzyme, in which the
presence of an exogenous inducer, tobacco smoke
affects transcription and translation and may
contribute to an UM phenotype, resulting in an up to
50% reduction in plasma concentration of Ads
Some CYP1A2 polymorphisms (rs4646425;
rs2472304; rs2470890) may also influence treatment
response to paroxetine
37. P-glycoprotein (P-gp) is a member of the ATP-binding
cassette superfamily of membrane transport proteins
encoded by the ABCB1 gene also known as the multidrug
resistance protein 1 (MDR1) gene.
P-glyco-protein 1 is found in various human tissues,
including the endothelial cells of the blood-brain barrier
(BBB) and is responsible for the efflux of many exogenous
and endogenous substances against a concentration
gradient influencing antidepressant concentrations in the
brain as well.
38.
39. Monoamine transporters Serotonin
Transporter (SLC6A4) The human serotonin
transporter (5-HTT) gene is potentially
involved in mood regulation and the great
majority of currently used ADs influences the
activity of 5-HTT, making it an ideal
candidate for pharmacogenetic studies.
40. A 44-bp insertion/deletion poly-morphism with 2 allelic
forms within the serotonin transporter gene promoter region
(5-HTTLPR) that could affect SLC6A4 expression was shown
to have functional significance with the long allele (l)
associated with two times higher 5-HTT expression in the
basal state compared to the s allele according to in vitro
studies
Caucasian subjects report that presence of the s allele is
associated with lower response and remission
41. According to the results of a recent GWAS study
cer-tain genetic variations of the noradrenalin
transporter may be associated with the risk of
MDD. In addition, the noradrenalin transporter is
the principal site of action of some ADs
42. It is assumed that dopaminergic mechanisms play an
important role in AD drug action, since AD drugs, in particular
dopamine/norepinephrine reuptake inhibitor bupropion and
specific members of SSRIs (mainly sertraline) modulate
activity of the dopamine transporter.
A 40-base pair VNTR polymorphism in the SLC6A3 gene,
encoding for the dopamine transporter (DAT) has been
associated with expression levels of the transporter.
43. Tryptophan hydroxylase
The tryptophan hydroxylase (TPH) gene encoding
the rate-limiting enzyme in serotonin synthesis has
been studied intensively in psychiatric disorders,
yielding mixed results.
44. The COMT enzyme is responsible for the inactiva-
tion of various catecholamines including dopamine,
adrenalin and noradrenalin.
The COMT gene has several allelic variants,
including the most extensively studied rs4680
variant.
A functional G to A SNP at codon 158 leading to a
Val to Met substitution was identified contributing
to a high activity Val/Val, intermediate activity
Val/Met, low activity in Met/Met genotype
45. MAO-A is one of the enzymes responsible for the
degradation of monoamine neurotransmitters. One
polymorphism in the promoter region of the MAO-A gene
consisting of a repetitive sequence (VNTR) has been
linked to variations in the biological activity and
consequentially serotonin concentrations.
Variants with 3.5 or 4 copies of the repeat sequence
(“MAO-A High”) are expressed 2-10 times more efficiently
than those with 2, 3 or 5 copies of the repeat
46. Monoamine receptors are among the most
plausible candidates for modulation of AD
response, since most ADs act to increase
monoamine concentration in the synaptic
cleft.
47. About 50 known SNPs have been described regarding
the 5-HT1A autoreceptor. One of the most intensively
investigated functional polymorphism (rs6295; a.k.a.
1019C/G) is in the promoter region of the gene for 5-
HT1A receptor (Stahl, 1994). The majority of results
suggests an effect of the rs6295 on treatment outcome
with several classes of ADs,
48. Three important common SNPs of the 5HTR2A gene are
102T/C (rs6313), 1438A/G (rs6311) and 452His/Tyr (rs6314).
Overall, several studies have found that rs6313, rs6311 and
rs6314 SNPs are associated with response to AD treatment,
Another genetic variant of the 5HTR2A gene (rs7997012) is
also associated with success of AD treatment.
49. According to our current knowledge, among the
different adrenergic receptor subtypes, the β1 and
α2a receptors seem to play a role in response to AD
treatment
A recently identified functional polymorphism
G(1165)C (a.k.a. rs1801253) in the ADRβ1 gene
(encoding adrenergic β1 receptor), resulting in the
amino acid variation Gly389Arg, has been linked to
enhanced coupling to the stimulatory Gs protein and
increased adenylate cyclase activation. This SNP might
be responsible for faster response to AD treatment
50. G Protein β3 subunit
The β3 subunit of the G protein is present in all cells of the body
and has a key role in the downstream signaling cascade
following monoamine receptor activation.
The C825T (a.k.a. rs5443) functional polymorphism is the
most investigated variant within the GNβ3 gene in this field. It
was associated with AD treatment response; particularly the T
variant seems to predict better AD response.
51. CRH Receptors (CRHR1 and CRHR2)
Corticotropin releasing hormone (CRH) is a potent mediator
of endocrine, autonomic, behavioral, and immune
responses to stress.
An association between the rs242941 G/G geno-type and
homozygous GAG haplotype of the 3 SNPs (rs1876828,
rs242939, and rs242941) and therapeutic response to
fluoxetine
Another study did not find associations between some
other variants of CRHR1 gene (rs110402; rs242937) and
treatment response to citalopram
52. The GENDEP study identified three SNPs
(rs852977, rs10482633 and rs10052957) which
may predict response to both ADs used in the
study (nortriptyline and escitalopram)
53. Despite of expectations fuelled by the role of CREB in the
pathogenesis of depression, the role of CREB1 variants in
AD response was not verified .
Furthermore, two SNPs (rs4675690; rs7569963) were
found to have a role in treatment-emergent suicidal
ideation in patients with MDD during citalopram
treatment, but only in males, suggesting a significant
gene x sex interaction
54. Chronic stress leads to decreased levels of BDNF
in the brain, and serum/plasma BDNF levels of
patients with mood disorders are decreased.
55. Results of the GENDEP study have raised the possibility
that that there is an association between rs10835210
variation in the BDNF gene and response to escitalopram
and a strong association between rs962369 in the BDNF
gene and an increase in suicidal ideation during AD
treatment (the same study identified some other
suicidality related regions in the BDNF gene
56. According to results of the STAR*D study an SNP
(rs1954787) of the GRIK4 gene encoding kainate
receptor subunit 1 (KA1; a.k.a. GluK4) was
associated with treatment response to citalopram
57. Despite the impressive potential of pharmacogenetics and
the great progress in the understanding of the
pathomechanism of MDD and the genetic influence both
on emergence of depression and on response to AD
treatment, the use of pharmacogenetics in current clinical
practice is still very limited,
58. in part due to inconsistent results and failure to replicate
several associations.
Another problematic issue is the complexity and
ultifactorial nature of the genetics underlying psychiatric
disorders and medication response. Since the therapeutic
mechanism of ADs is not well understood, it is difficult for
pharmacogenetic researchers to select “candidate” genes.
59.
60. Since chlorpromazine was first introduced into
clinical psychiatry, various kinds of
antipsychotics have been developed and used
for schizophrenia.
Clinicians, however, still have considerable
difficulty in choosing an appropriate
antipsychotic for certain patients due to the
inter-individual diversities of drug response.
61. Most antipsychotics are extensively metabolized by
cytochrome (CYP) P450s that are members of a
super-family of oxidative enzymes and that
constitute a major system for the oxida-tive
metabolism of therapeutic substances.
62. The CYP2D6 has been most extensively
investigated in the field of psychiatry, since
this enzyme is involved in the metabolism
of many antipsychotics and has many
genetic polymorphisms that influence the
function of the enzyme.
63. There are more than 70 variant alleles at
the CYP2D6 gene locus, including the two
most common variants, CYP2D6*4 and
CYP2D6*45, encoding non-functional
products.1 Other variants that reduce
activity, alter substrate specificity or
increase activity have also been described
64. Compared with efficient metabolizers (EM), poor
metabolizers (PM) show no or reduced CYP2D6
activity bypolymorphisms resulting in potentially
increased concentrations of metabolized drugs.
65. On the other hand, ultra rapid metabolizers
(UM) that can be found in 1% of Caucasians
often do not reach therapeutic concentrations
and require an increased dose. Pronounced
ethnic differences in the prevalence of both PM
and UM have been reported; e.g., the frequency
of PM is 5 to 10% among Caucasians, about 2%
in Asians, and 7–8% in Africans.
66. PMs have higher plasma concentrations of and suffer more
adverse effects from antipsychotics. The incidence of the
acute side effects of these drugs, including postural hy-
potension, excess sedation, or extrapyramidal symptoms, is
disproportionately in PMs.
On the other hand, it is not clear whether the development
of chronic side effects such as tardive dyskinesia is
associated with a reduced metabolizing capacity of CYP2D6.
67.
68. All receptor and transporter genes for
neurotransmitters as well as genes located down-
stream of the intracellular signaling pathways
can be considered candidate genes for the
pharmacodynamics of antipsychotics.
It is difficult to select a good candidate gene,
since the true mechanism of therapeutic action of
antipsychotics has not been clarified yet.
69. genetic polymorphisms in serotonin (5-HT)
and dopamine (DA) systems have been
extensively investigated in the
pharmacodynamics of antipsychotics
70. The first candidate gene examined with regard to
clozapine response was the DA4 receptor gene
(DRD4) because in addition to its high affinity for
clozapine, the DA4 receptor is abundant in the
prefrontal cortex, (a brain region thought to be
related to the cognitive dysfunction of schizophrenia),
and the DRD4 gene itself is highly polymorphic.
71. Among polymorphisms in the DRD4, the 48 bp
variable number of tandem repeats (VNTR) has
been the most extensively investigated, since the
VNTR was shown an in vitro study to influence
the sodium chloride sensitivity of clozapine-
binding and inhibition of c-AMP synthesis.
72. The DA3 receptor, which shares homologies with both
the DA4 and DA2 receptors, has generated interest,
since the DA3 receptor gene (DRDA3) has a known
functional polymorphism,Ser9Gly, that influences
dopamine binding. However, the association between
the Ser9Gly and clozapine response remains
controversial.
73. The DA2 receptor is a major site of the action of conventional
antipsychotics such as chlorpromazine and haloperidol, and of
some atypical antipsychotics such as risperidone. One
functional polymorphism (-141 Ins/Del) in the promoter
region, as well as missense variants including Ser311Cer and
an intronic variant (Taq 1 A), have been identified in the DA2
receptor gene (DRD2).
74. The -141 Ins/Del polymorphism that influences
the expression of the DRD2 was reported to be
associated with anxiolytic and antidepressive
effects during treatment with two conventional
antipsychotics,
75. Although theSer311Cer was shown to influence c-
AMP synthesis, it has not been associated with
clozapine or with a typical antipsychotic response.
The Taq 1A that is located in the intron of DRD2
and has been reported to influence the density of
the receptor was shown to have an association
with the acute effects of a selective DA2 receptor
antagonist, nemonapride, and haloperidol.
76. The 5-HT receptor genes have been regarded as
good candidates for pharmacodynamic stud-ies of
antipsychotics, since 5-HT mediated mechanisms
seem crucial to atypical antipsychotic drug action,
including that of clozapine.
77. An association between the silent polymorphism
102T/C in the 5-HT2A receptor gene (HTR2A) and
clozapine has been reported.
Hys452Tyr12 was shown to influence the
intracellular signal transduction of the 5-HT2A
receptor, as measured by Ca2+ mobilization
induced by 5-HT stimulation.
78. In addition to the 5-HT2A receptor, other 5-HT receptors,
such as 5-HT 2C and 5-HT 6, have also been investigated in
psychopharmacognetic studies because atypical
antipsychotics also have high affinity for these receptors.
The Ser23 in the 5-HT2C receptor gene influences m-
chlorophenylpiperazine (m-CPP), a nonse-lective5-HT2C
agonist, binding, in comparison with Cys23. Therefore, the
Ser23 may be consti-tutively more active and tends to be
more desensitized.
79. Not just one gene but multiple genes play a role in
complex phenotypes, including the clini-cal response to
medication. Arranz et al. published the most
comprehensive study to date of a pharmacogenetics
screening strategy: a combination of 6 out of 19
candidate gene variants (in 5-HT2A, 2C, 5-HT transporter
and Histamin 2 receptor genes) predicted response to
clozapine with a prediction level of 76.9%
80. Interindividual Variability in Clozapine
Pharmacokinetics and Response: A Focus on
Cytochrome P450-1A2 (CYP1A2)-Mediated Enzyme
Metabolism
81.
82. Clinicians almost always initiate antipsychotic drugs in
schizophrenia “a priori” . However, this may lead to ineffective
treatment, to the use of an additional antipsychotic or multiple
antipsychotics, to different adverse effects, and result in
increased morbidity and mortality.
This represents a real concern and calls for accurate scientific
methods that could be used to predict a reasonable
therapeutic response and also drug-induced side effects.
83. Personalized prescription or “tailoring drugs to a patient’s
genetic makeup” would be more than beneficial (de Leon
2009b). In the context of personalized prescription,
clinicians need to consider environmental, personal and
genetic variables when prescribing any medication.
According to de Leon, personalized prescription in the
clinical practice may be described as personalized
selection of the drug and as personalized dosing
84. In personalized dosing the knowledge of
pharmacodynamic and pharmacokinetic dosing
properties should be applied.
85. At the present, in psychiatry there are five
pharmacogenomic tests that are currently
available on the market or are ready to be
introduced.
However, three of the five tests have not published
complete details concerning the genes used in
them
86. CYP 450 Test employs microarray technology for cytochrome
P450 (CYP) 2D6 and CYP 2C19 genotyping (de Leon et al.
2009c).
Genomic DNA is extracted from a whole-blood sample to
identify 27 alleles in CYP2D6 that are associated with four
CYP2D6 phenotypes, and to identify three alleles in CYP2C19
that are associated with two CYP2C19 phenotypes (de Leon
et al. 2009c).
The genotypes are then translated with software algorithms
into a predicted phenotype, which is indicative of the
CYP2D6 and CYP2C19 enzymatic activity.
87. One company offers a genetic test for the
determination of high (1,5%) or low (0,5%) risk of
drug-induced agranulocytosis.
The test can make a valuable prediction in the
treatment with clozapine, but does not obviate the
need for regular monitoring and has not a
significant impact on routine practice.
88. A new system, called PhyzioType System uses an
ensemble of DNA markers from several genes to
predict an individual’s risk of developing some
adverse drug reactions. The clinical applica-bility
of this array is still under investigation.
A recent study describes an array containing
probes to identify genetic variants for the risk of
hyperlipidemia.
89. PhyzioType System uses
Arranz et al. tried to combine genetic
information on the prediction of response to
clozapine. The prediction level in British
Caucasian patients on long-term treatment
was 76%, but the results were not replicated
in German cohort.
