Pharmacogenetics Flashcards
Pharmacogenetics goal for non-responders:
improve Drug Efficacy
Pharmacogenetics goal for toxic responders
improve Drug Safety
He developed the concept of chemical sensitivity
Archibald Garrod
In a sample case study, they discovered that intake of primaquine causes adverse drug reactions among African-Americans where they develop G6PD deficiency which leads to:
hemolytic anemia
The enzyme homogentisate 1,2 – dioxygenase mediates the breakdown of the amino acids:
Phenylalanin and tyrosine
alcaptonuria
excretion of homogentisic acid
homogentisic acid - (2,5 dihydroxyphenylacetic acid) an intermediate in the catabolism of aromatic amino acids such as phenylalanine and tyrosine
Mendel’s Four Principles of Inheritance
- ) Genes in pairs
- ) Dominance and Recessiveness - dominant gene will be expressed unless recessive genes are homozygous
- ) Principle of Segregation - one allele is contributed by each parent during meiosis
- ) Principle of Independent Assortment - combination of mother and father genes resulting to own individual traits
Start codon
AUG
Stop codons
UAA, UAG, UGA
Basic Patterns of Inheritance
MAXA
> Mitochondrial - ex. aminoglycoside-induced deafness
Autosomal Dominant
X-linked - ex. G6PD deficiency, Pyridoxine sensitive anemia, Vasopressin resistance
Autosomal Recessive
Factors Affecting Drug Sensitivity
Genetics, Disease, Age (geriatric, preterm, clinically ill are most sensitive), Drug-related factors (Pharmaceutical Formulation, Route of administration, Drug Interaction, Environmental Factors)
An anti-hypertensive drug used as a probe drug to identify the activity of CYP450
Debrisoquine
TRUE OR FALSE. Phenotyping can produce false results.
TRUE. Phenotyping is a direct measure of gene expression but it is subject to artifacts -> false results.
TRUE OR FALSE. Phenotyping provides a more reliable method for predicting whether or not an individual is a candidate for polymorphic metabolism.
FALSE. Molecular Genotyping is more reliable.
Polymerase chain reaction (PCR) and Restriction fragment length polymorphism mapping (RFLM) are methods for:
Molecular Genotyping
Molecular Genotyping Services are primarily driven by these three requirements:
DEPs
need to:
- DETERMINE SAFETY AND EFFICACY of an investigational new drug prior to approval
- ESTABLISH an individual’s GENETIC PREDISPOSITION to a disease state
- PROTECT patients AGAINST possible ADR’S by identifying poor metabolizers at the inception (initial laboratory studies of drug) of drug therapy.
TRUE OR FALSE. Polymorphic: frequently occurring monogenic variants occurring at a frequency < 1%.
FALSE. >1% dapat. Kung less than 1% considered insignificant ang variation.
Most common DNA Sequence Variation.
Single Nucleotide Polymorphisms (SNP)
Types of SNPs
Missense - change results in a codon that codes for a different amino acid.
Nonsense - results in a premature stop codon.
Frameshift by Addition
Frameshift by Deletion
TRUE OR FALSE. To be important SNPs must affect either function or amount of a protein
TRUE.
Goal is to determine the sequences of the 3 billion chemical base pairs that make up the human DNA.
Human Genome Project
Differentiate Pharmacogenetics from Pharmacogenomics.
Pharmacogenetics is A SUBSET of pharmacogenomics and is defined as the study of genetically controlled variations in DNA SEQUENCE as related to drug response.
Pharmacogenomics is defined as the study of variations of DNA AND RNA CHARACTERISTICS as related to drug response.
Poor metabolizers (PM) with slower than usual drug metabolism can lead to ______ blood levels causing _________.
HIGH; TOXICITY
Why does therapeutic failure happen in people who are Ultra-Fast metabolizers?
Too fast drug metabolism -> Drug excreted rapidly -> too low blood levels -> therapeutic failure
Ultra-Fast Metabolizers, when they use prodrugs:
a. Poor Efficacy
b. Adverse Drug Reaction (due to toxicity)
b.
In Ultra-Fast Metabolizers, prodrug is rapidly converted to active component eventually reaching high levels in the blood leading to toxicity. (Opposite pag normal drug. Pag normal drug, therapeutic failure naman kasi mabilis ma-metabolize and ma-excrete.)
Giving Debrisoquine among CYP2D6 Poor Metabolizers results to:
HYPOTENSION. Matagal na-metabolize ang debrisoquine kasi nga poor metabolizer so increase in blood levels leading to marked hypotension. Eventually, magllead to Delayed Toxicity (just like what happens when Poor Metabolizers use drugs even at theoretically therapeutic dose -> kaya important ang Pharmacogenetics para malaman mo kung Poor or Ultra-Fast Metabolizer ba siya.)
Pattern of Inheritance of G6PD Deficiency
X-linked
Giving Primaquine to patients with G6PD Deficiency would result to:
Hemolytic Anemia and eventually, severe pallor. (Primagquine is an anti-malarial drug)
Incidence of G6PD deficiency in Filipinos:
13%.
Micronesians - >1% Chinese - 2% African-Americans - 10% Javanese - 13% Indians-Parsees - 16%
Drugs and chemicals unequivocally demonstrated to precipitate hemolytic anemia in Subjects with G6PD
Deficiency
A-M-4N-P-4S
(Lahat ng S ay Sulfa-)
o Acetanilide
o Methylene blue
o Nalidixic Acid
o Naphthalene - accidentally ingested mothballs
o Sulfapyridine
o Sulfanilamide
o Sulfamethixazole
o Primaquine
o Sulfacetamide
o Nitrofurantoin
o Nitrates – salitre-treated meats (tocino, longganisa)
Unusual Response to Halothane:
Malignant Hyperthermia
Mutations in what receptor can result to unusual responses to the anesthetic, Halothane?
Ryanodine
Classic presentation of malignant hyperthermia following use of halothane.
rapid rise in body temperature, muscle rigidity, tachycardia, rhabdomyolysis (muscle wasting), severe acidosis, hyperkalemia - THINK EXAGG POTENTIATION OF Calcium, which is the effect of Halothane on patients with mutations.
Antidote to unusual response to halothane
L.V. Dantrolene
Patients with Warfarin (anticoagulant) resistance may require _____ times higher than the recommended therapeutic dose due to genetic defects.
7-20 times
Mutations in this multiprotein complex leads to Warfarin resistance.
VKORC1 ( vitamin K epoxide reductase multiprotein complex)
For patients with Folate Resistance, how many times the usual daily recommended dose is required?
40-1000 times.
TRUE OR FALSE. In drugs with wide therapeutic range, individualizing the dose is still important.
FALSE. The opposite is true. Individualizing the dose is not necessary for drugs with wide therapeutic range.
The elevated level of isoniazid (INH) in tissues of slow
acetylators will inhibit the metabolism of?
PHENYTOIN. Susceptibility of slow acetylators to phenytoin will be enhanced when phenytoin and isoniazid are given together -> inhibits metab of phenytoin by Cytochrome P450 (only in slow acetylators) -> accumulation of phenytoin.
TRUE or FALSE. Individualizing therapy is important for drugs with a narrow therapeutic range (e.g., Digitalis or Digoxin, antineoplastic agents)
TRUE. Obvious =))
Increased risk of cancer is associated with which of the following polymorphisms?
a. CYP (2A1, 1A2, 2E1)
b. Glutathione transferases (GSMT1, GSTT1)
c. Epoxide hydrolase
d. NAT2 – N-acetyl transferase 2
e. AOTA
E. AOTA. According to the trans =))
TRUE or FALSE. Lipophilic compounds are easy to remove from the body.
FALSE. Lipophilic compounds are difficult to remove from the body. They tend to remain inside tissues and cells because they can easily penetrate cell membranes.
Mechanisms of variation include:
a. Modification of absorption of the xenobiotic
b. Modified metabolism that results in modification of rate, pattern of elimination, detoxification or activation of a given xenobiotic
c. Modification in the abundance, affinity or function of a target enzyme or receptor
d. AOTA
d. AOTA. Memorize mo yung tatlo.
Modification of
ABSORPTION METABOLISM - rate, pattern of elimination, detoxification or activation of a given xenobiotic ABUNDANCE AFFINITY FUNCTION OF A TARGET ENZYME OR RECEPTOR
Deficiency of this enzyme is inherited as an autosomal recessive trait and occurs with increased frequency in Inuit and Alaskan Native Americans. It was manifested in the story of the cyanotic “blue” family.
methemoglobin reductase
Administration of this drug to Slow Metabolizers would result to dramatic fall in blood pressure.
Debrisoquine
TRUE or FALSE. If the metabolism of a drug is shunted from the harmless pathway, formation of toxic metabolites could cause toxic manifestations.
TRUE. Example, paracetamol overdose overwhelms
glucoronidation and sulfation so metabolism is shunted to Cytochrome P450 metabolism (Phase I) eventually causing the increase in the toxic metabolites.
“Silent” variants of serum cholinesterase associated with:
succinylcholine
A variant form of ADH produced at the ADH2 locus exhibits much higher catalytic activity than the typical subunit. It contains a variant beta 2 subunit –commonly referred to as the:
ATYPICAL ADH.
The atypical B2 subunit differs from the typical by CGC to CAC transition resulting in an Arg47His substitution in beta 2 subunit (B2)
This mutation is responsible for:
- higher ethanol Vmax of the atypical
- higher Km for the homozygous B2B2 enzyme
*I-remember mo itong higher Km for homozygous B2B2 enzyme. Basta associated ito with molecular aspect ng alcohol dehydrogenase.
Alcohol dehydrogenase (ADH) variations have the highest ethnic distribution in: (which nationality)
Swiss - 20%
5-10% of English, 9-14% of Germans.
Deficiency of this enzyme leads to the accumulation of acetaldehyde which is manifested as the characteristic “flushing” and feelings of discomfort in Asians when ethanol is ingested.
ALDH2 - Aldehyde Dehydrogenase 2
*8-45% in Asians.
Cyclophosphamide polymorphic biotransformation of antineoplastic agents causes:
cystitis.
In simpler terms: pharmacokinetically abnormal metabolism of antineoplastic agents = CYSTITIS
The major toxic manifestation in a homozygous DPD-deificient person given 5FU (5-fluorouracil) occurs mainly in the:
in rapidly dividing tissues such as the BONE MARROW.
*DPD - Dihdydropyrimidine dehydrogenase deficiency
Mephenytoin hydroxylation polymorphism is a variation occuring in two distinct phenotypes (poor metabolizers and extensive metabolizers) which is based on the person’s ability to hydroxylate Mephenytoin to 4-OH-mephenytoin, a metabolic process which is mediated by which CYP?
CYP2C19.
Basta pag lumabas ang mephenytoin, CYP2C19 na yan!
Parathion (an organophosphate) poisoning occurs in patients with this polymorphism:
Paraoxon Polymorphism (also called PON1 or PON2 polymorphism)
*Parathion poisoning was first observed in an outbreak of poisoning from barley contaminated with parathion in September 1959.
Personal or family history of an adverse drug reaction to these THREE choline ester compounds may be the only clue suggesting pseudocholinesterase deficiency.
Pseudocholinesterase deficiency - SUCO-MI (SUKO MI)
SUccinylcholine, COcaine, MIvacarium
- Another thing to help you remember: Pseudocholinesterase causes the hydrolysis of succinylcholine
- HISTORY-TAKING is therefore very important in the documentation of pseudocholinesterase deficiency
Gene coding for the enzyme is located at the E1 locus on the long arm of chromosome 3
Pseudocholinesterase
Manifests as slightly prolonged duration of paralysis
(>5 minutes but <1 hour), following administration of succinylcholine
Pseudocholinesterase Deficiency
- Basta Pseudocholinesterase Deficiency, i-associate mo na agad sa succinylcholine.
Normal Dibucaine Number (DN) for the homozygous typical genotype (EuEu) is:
80%.
The Dibucaine Number is the percent inhibition of hydrolysis of benzyl choline caused by the addition of dibucaine to the pseudocholinesterase enzymatic assay.
This Info is under -> Dibucaine-resistant genetic variant form of Pseudocholinesterase Deficiency
Individuals homozygous for the atypical dibucaine resistant genotype (EaEa) have a DN of: 20%
20%.
Typical genotype for dibucaine resistance: EuEu
Atypical: EaEa - a for atypical.
Most common of all the abnormal pseudocholinesterase genotypes.
Heterozygous genotype for Dibucaine resistance (EuEa)
Found in 2.5% of the general population, making it more common than all other abnormal pseudocholinesterase genotypes combined.
TRUE or FALSE. The goal of Pharmacogenetics is to deliver the right medicine to the right patient.
FALSE. The goal of Pharmacogenetics is to deliver the right medicine at A RIGHT DOSE to the right patient.
Super important ng Dose =)
TRUE or FALSE. The heterozygous fluoride-resistant genotype is usually clinically insignificant unless accompanied by a second abnormal allele or by a coexisting acquired cause of pseudocholinesterase deficiency.
TRUE.
In general, applicable ito sa lahat ng pseudocholinesterase-partially deficient patients. Kailangan ng concomitant acquired cause of pseudocholinesterase deficiency bago maging clinically significant.
Identified by its percent inhibition of benzyl choline
hydrolysis when fluoride is added to the pseudocholinesterase enzymatic assay.
Fluoride-resistant pseudocholinesterase enzyme variant
This homozygous fluoride-resistant genotype exhibits mild to moderate prolongation of succinylcholine-induced paralysis.
Most severe of all atypical gene alleles for the Pseudocholinesterase genotype
SILENT GENOTYPE.
Gene mutations by frameshift or stop codon mutations, resulting in no functional pseudocholinesterase enzyme synthesis at all. BANG. Ibig sabihin mas matagal yung muscle paralysis after a dose of succinylcholine -> abot 8 hours.
SILENT GENOTYPE occurs in only _ out of 100,000 individuals.
1 out of 100,000.
FROM TRANS: Occurs in only 1 in 100,000 individuals who are homozygous for the silent Es genotype (this
was HIGHLY emphasized!), with no detectible
pseudocholinesterase enzyme activity
Since the DNA sequence of the pseudocholinesterase gene and its amino acid structure is known, atypical alleles now can be identified by:.
PCR Amplification.
- > using DNA extracted from leukocytes in a blood sample
- It is important to consult with a geneticist to help identify the specific atypical genotype alleles contributing to pseudocholinesterase deficiency.
Tandaan:
Atypical genotypes of Pseudocholinesterase Deficiency:
- Dibucaine-Resistant Genetic Variant Form
a. Homozygous typical (EuEu),
b. Homozygous atypical (EaEa) and \
c. Heterozygous (EuEa) -most common - Fluoride-resistant pseudocholinesterase enzyme variant
60% for the EuEu genotype and is 36% for the EfEf genotype - Silent Type - most severe
Fish Odor Syndrome is due to:
Excessive excretion of trimethylaminuria (TMA)
If you give debrisoquin to a hypertensive patient and there was no effect, the phenotypic presentation is
a. Poor Metab
b. Ultrarapid Metab
ULTRARAPID METABOLISM. The drug is excreted before it reaches the therapeutic range so, no effect.
Type of metabolizer with standard metabolic activity, appropriate therapeutic outcome with standard dosages and minimal or absent toxicity.
EXTENSIVE.
Poor metabolizer: accumulation of parent drug -> toxicity, opposite for prodrugs -> therapeutic failure
Ultrarapid metabolizer: low blood levels of parent drug -> therapeutic failure. Opposite for prodrugs. -> toxicity
Phenotypic outcomes of NAT2 polymorphism include
higher incidences and/ or severity of adverse drug reactions (ADR) to:
SPHI - Sulfamethaxazole, Procainamide, Hydralazine, Isoniazid
- pag NAT2 polymorphism Adverse Drug REaction (ADRE) = Spy sa PHI = SPHI
Many of the aromatic and heterocycluc amine
CARCINOGENS are both activated and deactivated by
acetylation reactions catalyzed by:
NAT2
Fast Acetylator vs. Slow Acetylator
If they smoke tobacco they have an 8-fold higher risk of cancer.
SLOW ACETYLATOR.
Slow acetylators who smoke tobacco have an 8-fold
higher risk of cancer (compared to their rapid acetylator smoking counterparts) due to the INABILITY TO DETOXIFY AROMATIC AMINES in tobacco smokers.
Fast Acetylator vs. Slow Acetylator
are at an increased risk of colon cancer if they eat lots of cooked meats.
FAST ACETYLATORs are at increased risk of colon cancer from the acetylation of heterocyclic amines
found in cooked meats.
Fast Acetylator vs. Slow Acetylator
More likely to develop peripheral neuropathy
SLOW ACETYLATORs
Patients with slow clearance of the drug (via acetylation) may require reduced dosages to avoid toxicity of isoniazid. Isoniazid toxicity + pyridoxine depletion = peripheral neuropathy
Fast Acetylator vs. Slow Acetylator
More likely to develop liver cancer.
FAST ACETYLATORs
- Filipinos in general
Xenobiotics Subject to Polymorphic Acetylation
HACD! (Hacked)
Hydrazines, Arylamines, Carcinogenic Arylamines, Drugs metabolized to amines
This allele is associated with rapid acetylators.
NAT2*4
Slow acetylators:
NAT25B
NAT26A (M1 & M2)
NAT2*14A
Toxicity following administration of 6-mercaptopurine (6-
MP), a type of thiopurine drug, will result if the patient has this polymorphism.
Thiopurinemethyltransferase polymorphism (TPMT)
This polymorphism is found in ALL (Acute Lymphoblastic Leukemia)
Thiopurinemethyltransferase (TPMT) polymorphism
Patients with Acute Lymphoblastic Leukemia (ALL) taking daily 6-mercaptopurine (6-MP) will develop:
myelosuppression.
TPMT polymorphism is found in ALL, therefore, the patient has undetectable intracellular activity of TPMT. Lack of TPMT activity produced higher concentrations of the 6-MP cytotoxic drug metabolites after administration -> myelosuppression
TRUE or FALSE. Trial and Error is the current practice in the application of pharmacogenetics.
TRUE. Ito yung practice talaga. Bigay ng standard dose. Kung walang effect -> increase dose or change drug. Kung toxic, increase dose or change drug
DRUG-DISEASE-GENE
Herceptin-Breast Cancer-?
HER2
DRUG-DISEASE-GENE
6-MP - ? - TPMT
ALL - Acute Lymphoblastic Leukemia
DRUG-DISEASE-GENE
? - Melanoma - Unpublished
Melacine
DRUG-DISEASE-GENE
5- Fluorouracil - ? - TS
Colorectal Cancer
Using an individual’s genetic profile to predict response to certain drugs
PHARMACOGENOMICS
Pharmacogenetics - study of genetic variations related to drug metabolism.
Treatment Decisions Using Pharmacogenetics
For patients with same diagnosis, Treat:
Responders & Patients not predisposed to toxicity
Treatment Decisions Using Pharmacogenetics
For patients with same diagnosis, Remove:
Non-responders and Toxic responders
to avoid and further study possible ADRs
