Receptor and other drug target pharmacogenetics Flashcards
what is the difference between polymorphisms in receptor and in metabolic proteins
you don’t see complete absence of the protein in receptors
what is the two ways that polymorphism can affect G-protein linked receptors
Either the receptor or the coupling process of the G-protein
How are polymorphism studied compared to metabolic
- Not able to study phenotype in same way as metabolic
- scanning genes by sequencing
- can use knock out mice (maybe?)
How is coding sequences used to study polymorphisms
Express variant in suitable cell line and compare function (response to
agonist or antagonist) with wild-type
How are upstream polymorphism used to study polymorphisms
- reporter genes (luciferase) are place in a promoter region and then placed in a vector and transfected into cell line
- can use alkaline phosphatase (less sensitive, No need to lyse cell as product in released into medium)
What is B2-adrenergic receptor
-product of introless gene with coding region of 1239bp
what are the polymorphisms in the coding region of with B2-adrenergic receptors
9 known polymorphisms, resulting with 4 amino acid substitutions
Arg16Gly
Gln27Glu
Val34Met
Thr164Ile
what is the polymorphism in the leader peptide of B2-adrenergic receptor
Arg19Cys
how many upstream polymorphism are associated with B2-adrenergic receptor
7
what is a haplotype
combination of alleles on a
particular chromosome. Often will get linkage
with some polymorphisms occurring together
What are the 3 common haplotypes of B2-adrenergic receptor in Europeans
2,4 & 6
What haplotypes of B2-adrenergic receptor are seen in African americans
1 is also common as well as 4 and 6
2 is rare
What haplotype of B2 adrenergic receptor has the smallest change in FEV when B agonist is administered
4/4
both AA at 16 is arginine
What haplotype of B2 adrenergic receptor has the largest change in FEV when B agonist is adminstered
4/6
One AA at 16 is arginine and one is glycine
which haplotype of B2-adrenergic receptor responed better to placebo than to salbutamol
4 - Arg
where are B1 receptors mainly located and what are the main type of drugs associated
- in the adrenoreceptor in the heart
- b blockers = Atenolol
what is the main polymorphism associated with B1 adrenoreceptors and what is the frequency of theses variants
- Gly389Arg amino acid
- Gly variant has frequency of 0.26, Arg 0.74
what is the effect of Gly389Arg polymorphism in B1-adrenorecptors
Arg form shows enhanced Gs protein interaction and increased adenyl
cyclase activation
what is the pharmacological effect B1 adrenergic receptor polymorphims
Patients homozygous for the Arg have a better response to metoprolol
what is the gene for the enzyme for coumarin anticoagulants (warfarin)
VKORC1
what is the protein which is the target for warfarin
Vitamin K epoxide reductase
True/False - There should be no difference between patients in the dosing of warfarin to achieve good clotting
False - individuals have varying doses
there are also some patients who are warfarin resistant
what is the normal dose of warfarin
- 5 mg/day
- each patients should be titrated to measure clotting though
what is the vitamin K cycle
-Vitamin K is needed as a cofactor for carboxylase enzyme
- the process to make the clotting factors then generates vitamin K epoxide
- this must be regenerated to Vit K by VKOR
what is the two polymorphisms in VKORC1
G1639A - in upstream region
C1173T - in the first intron
how many exons are in VKORC1 and how
3
True or false -Polymorphisms in VKORC1 are inherited independently
False, due to small size, two polymorphism are almost always inherited together
G-1639A and C1173T form part of haplotype associated with __ warfarin dose
lower
which VKORC1 haplotype has higher expression of VKOR
Homologous for wildtype
In the overall population, what is most people’s genotype (VKORC1)
Heterozygous
what is the only group of people who can take more than 8mg warfarin per day
homozygous for wildtype
what is warfarin resistance
patients doesn’t respond to W or needs unusually high dose (>10mg/day)
- Normally its due to non-compliance
- some patients have mutations in coding region of VKORC1
- affects W binding but not Vit K epoxide reduction
True or false - due to few mutation which could cause pharmacodynamic warfarin resistance, population frequency is very low
False
There are several mutation
This means screening prior to treatment is not considered due to rarity
What is the mutation which is more common in Isreal, Egypt and Ethiopia which can cause warfarin resistance
D36Y
What are the two genes which effects warfarin dose
CYP2C9 & VKORC1
Which of the two genotypes relating to Warfarin dose, causes a patient to require the highest dose
Wildtype - CYP2C9
Wildtype - VKORC1
Effects of VKORC1 genotype affecting warfarin dose is seen less in subjects with CYP2C9(2/3) or CYP2C9(3/3) why ?
There are less people who have these genotypes therefore less variation
All cystic fibrosis patients have defect in __ gene which codes for __ involved in __ transport
CFTR
ion channel
Cl-
what is the most common genetic defects involved in Cystic fibrosis
F508 (single amino acid [phenylalanine] deleted)
so the protein is not inserted into the cell membrane
5% of patients have this genetic polymorphism which causes the channel to reach the cell surface but not transport Cl-
G551D - channel no longer responds to ligand
what is the cellular effect of the Cystic fibrosis polymorphism Class 3 (G551D)
missense mutation results of AA substitution which disrupts regulation of teh CRFT channel
which drug reverses the G551D mutation in CRFT channel
Ivacaftor
