pharmacogenomics implication of risk snps in diabetes

Pharmacogenomic implications

of risk SNPs in type 2 diabetes mellitus

Dr Muhammad Huzaimi HaronTrainee Lecturer in Pharmacology

Pharmacology CME 28 March 2011

Introduction

T2DM revisit

What are SNPs?

Individual SNPs conferring T2DM risk

SNPs and Pharmacogenomics

What lies ahead

Take home message

Outline

Genetic component to diabetes High concordance rate between monozygotic

twins Different prevalence between populations Different effect of traditional risk factors

Single nucleotide polymorphisms (SNPs) Common Functional Heritable?

Introduction

Revisit: T2DM pathogenesis

T2DM

Hyper-glycaemi

a

Insulin sensitivit

y

Beta-cell dysfuncti

on

Revisit: T2DM pathogenesis

T2DM

Hyper-glycaemi

a

Insulin sensitivit

y

Beta-cell dysfuncti

on

Incretins

K+ channel

Incretins

T2DM: Global Epidemic!

Afric

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T2DM: Global Epidemic!

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an

East

Med

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Amer

icas

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pean

Sout

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sia

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Increasing prevalence 6.3% in 1986 (NHMS I) 11.0% in 2006

(MyNCDS-1) NHMS II (1996): 8.3% (>30 yrs old) NHMS III (2008): 11.6% (>18) 14.9% (>30)

39% did not know they were diabetic! 83% of 18-30yr old diabetic newly diagnosed!

Ethnic discrepancy (NHMS III)

Indian highest (19.9%) Malay (11.9%) and Chinese (11.4%)

T2DM: Back home…

High prevalence of undiagnosed DM in younger age group (18 – 30 years old)

Increasing prevalence despite:1. Health awareness campaigns2. Increasing education and information levels

Worrying signs in NHMS III

Need for a better screening program?

Single Nucleotide Polymorphism

A C G T C T G A

AAT

TCC

G G

T

A

DNA seq change

Coding region

mRNA seq change

Intronic

mRNA processing

altered

Exonic

AA seq change

Changes in protein

Non-coding region

mRNA transcription

alteration

Implication of SNPs

Variations in how body handles glucose

AbsorptionRate of emptying of stomach

DistributionAction of insulinMetabolism

Alteration in metabolic pathwaysDisposition

Excretion of excess

How SNPs confer risk?

Year Gene Description SNPChro-

mosome

Major / minor allele

Phenotype

Beta cell

function

Insulin action

2000 PPARGPeroxisome proliferator-activated receptor gamma

rs13081389 3 A/G Reduce

d

2003 KCNJ11Potassium inwardly-rectifying channel, subfamily J, member 11

rs5215 11 C/TReduce

d

2006 TCF7L2 Transcription factor 7-like 2 rs7903146 10 C/TReduce

d

2007 CDKAL1CDK5 regulatory subunit associated protein1-like 1

rs10440833 6 A/TReduce

d

2007HHEX/IDE

Haematopoietically expressed homeobox / insulin-degrading enzyme

rs5015480 10 C/TReduce

d

2007 SLC30A8Solute carrier family 30 (zinc transporter), member 8

rs3802177 8 C/TReduce

d

2007CDKN2A/B

Cyclin-dependent kinase inhibitor 2A/B rs10965250 9 A/GReduce

d

2007 IGF2BP2Insulin-like growth factor 2 mRNA binding protein 2

rs1470579 3 A/CReduce

d

2007 FTO Fat mass and obesity associated rs11642841 16 A/C Reduce

d

2008 KCNQ1Potassium voltage-gated channel, KQT-like subfamily, member 1

rs231362, rs163184

11A/C, G/T

Reduced

SNPs conferring risk to T2DM

Protein: transcription factor 7-like-2 Gene on long arm of chromosome 10 Nuclear Wnt pathway

Controls expression of downstream genes Proglucagon (Ni et al, 2003) – promote expression in

intestinal L-cells mRNA silencing of TCF7L2: apoptosis of beta-cells

(Shu et al, 2008) proliferation, GSIS Reduced levels lead to defective insulin granule

exocytosis (da Silva Xavier et al, 2009)

TCF7L2 and T2DM

Multiple SNPs in multiple population rs7903146 rs12255372 rs4506565 rs11196205 rs7901695 rs290487

Intronic

TCF7L2 SNPs

Effect of SNPs on: Expression of TCF7L2 gene

Increased in pancreatic beta-cells (Lyssenko et al, 2007)

Expression of other genes Proglucagon – reduced in pancreatic L-cells (Yi et al,

2008)

Impaired GLP-1 synthesis Its protein levels: unknown Glucose handling

Blunting of incretin effect (Lyssenko et al, 2007; Schafer et al, 2007)

Reduction in pro-insulin conversion (Stancakova et al, 2009)

Increased hepatic gluconeogenesis (Pilgaard, 2009)

TCF7L2 SNPs and T2DM

Icelandic carriers of SNPs at increased risk of T2DM (Grant et al, 2006)

Dose-dependent Heterozygous carrier of T allele of rs7903146: OR

1.5 Homozygous carrier: OR 2.1

Replicated in various Caucasian and Asian populations However with differing impact due to different

allele frequencies

Impact on T2DM risk

Malaysian population No large scale data Known data collected from UMMC 2009-2010

from Malay, Chinese and Indian patients and non-diabetic volunteers

Case-control study of 800 people

Impact on T2DM risk

Type 2 DM Risk AnalysisTCF7L2SNP

Subject Minor allele frequency

p-value OR [95% CI] *of wildtype vs mutant allele

rs7903146 DiabeticNon-diabetic

0.160.10

0.0061 1.73 [1.17-2.58]


0.130.06

0.0010 2.14[1.35-3.40]


0.810.88

0.0047 0.61[0.43-0.86]


0.160.08

0.0013 2.11[1.33-3.36]


0.850.92

0.0025 0.49[0.31-0.79]

* Statistical test used: chi-square test

Type 2 DM Risk AnalysisTCF7L2

SNPSubject Genotype frequency (%) OR [95% CI]*

WT vs HZ genotypeWT Ht Mt


7283

2515

32 1.66

[1.13-2.44]rs12255372 Diabetic

Non-diabetic7790

208

32 2.37

[1.43-3.93]rs11196205 Diabetic

Non-diabetic74

2417

6979

0.95[0.80-1.12]


7386

2311

43 2.16

[1.31-3.56]rs7901695 Diabetic

Non-diabetic43

2311

7386

1.06[0.84-1.34]

* Statistical test used: chi-square test

1. TCF7L2 SNPs increase the risk of T2DM in a Malaysian population

2. The minor allele frequencies observed are: much lower than in Caucasian and Indian

population (Grant et al, 2006; Chandak et al, 2007)

higher than in Japanese population (Miyake et al, 2008)

Impact?

Summary from Malaysian data

KCNJ11

Codes for component of ATP-sensitive K+ channels on beta-cells (Kir6.2 subunit)

Mutations caused monogenic forms of DM

SNP (rs5215) cause defect to subunit K+ channels fail to open in response to rising

ATP:ADP ratio Failed exocytosis of insulin granules (reviewed by

Florez, 2008)

Other SNPs

KCNQ1

Encodes for a voltage-gated K+ channels needed for repolarisation phase of cardiac action potential This channel also found on intestinal L-

cells

SNPs (rs231362, rs163184) cause impaired incretin effect Reduction in GLP-1 secretion by L-cells (Tan et al, 2009)

Other SNPs

PPAR2 Codes for nuclear receptor Involved in lipid and glucose homeostasis,

differentiation of lipocytes, FA storage

SNP confers protection against T2DM Increased insulin sensitivity Lower BMI Higher HDL Lower BP Reduced MI risk

Other SNPs

Pharmacogenomics

Different DNA sequence, different response! Drug-metabolizing enzymes

Cytochrome-p450 family, eg CYP2C9 and sulfonylureas

Statement 1:

SNPs conferring risk affect glucose handlingStatement 2:

Glucose handling modified by drugs

Can risk SNPs alter drug response?

GoDARTs study (Pearson et al, 2007)

900 patients on a sulfonylurea Treatment failure: HbA1c >7% after 3 – 12

months of initiation Adequate control of confounder

SNP carrier 2 times more likely to encounter treatment failure – even after adjusting for baseline HbA1c

TCF7L2 SNPs and Sulfonylurea

rs7903146 rs12255372 rs11196205 rs4506565 rs79016950123456789

10

WTHZMt

TCF7L2 SNPs

HbA

1c (%

)

*

* *** *

* P<0.05, ** P<0.01

Genotypic comparison of HbA1c levels (Metformin+Sulfonylurea, n=113)

Genotypic Comparisons of Achievement of HbA1c target

Metformin + Sulfonylurea (n=29/113)

WT HZ Mt P-value(2)

rs7903146 83 10 7<0.001rs12255372 86 14 0

rs4506565 86 7 7rs7901695 7 7 86

<0.001rs11196205 10 4 86

WT: Wildtype, HZ: Heterozygous, Mt: Mutant

Sesti et al, 2006

525 patients treated with sulfonylurea, either alone or combination with metformin

Secondary failure: those requiring insulin therapy despite combination therapy

Adequate control of confounders SNP carrier more likely to get secondary failure

with sulfonylurea therapy Sulfonylurea-stimulated insulin secretion lower

in pancreatic islets carrying the SNP

KCNJ11 SNPs and Sulfonylurea

He et al, 2008

100 newly diagnosed Chinese patients, treated with repaglinide over 24 weeks

SNP carriers had greater reduction in FPG and HbA1c levels

SNP carriers had better improvements of HOMA-B

KCNJ11 SNP and Repaglinide

Kang et al (2005) Improved response to rosiglitazone in

heterozygous SNP carriers Greater drops in FPG and HbA1c

PPAR2 SNP and

is still uncertain

Identification of risk SNPs Need cohort studies, long term follow-up Involvement of epigenetics, CNVs

Pharmacogenomics Better-designed clinical trials, controlling for

confounder

Promise of personalised medicine in DM?

The future

Importance of genetic factors/variations in conferring risk to T2DM is evident

Response to antidiabetic medications is heavily influenced by genetic variations as well!

However, the specifics are still missing/unclear – lots of “research holes” yet to be filled…

Take home message

THANK YOUfor your kind attention

Incretins and GSISGlu

Pancreatic β-cells

GLP-1

GIP

GluGlu

Glu

Ins

Small intestine

lumen

Glu

Vasculature

Cell

Done

GSIS and Incretins: An Overview

• GSIS: glucose stimulated insulin secretion• Accounts for majority of postprandial insulin release• Earliest defect leading up to T2DM

• Incretins• Intestinal peptide hormones• Released upon detection of glucose in GIT• Glucagon-like peptide-1 (GLP-1)• Glucose-dependent insulinotropic polypeptide (GIP)

pharmacogenomics implication of risk snps in diabetes

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