The Genetic Epidemiology of Complex Diseases: Myopia

Eric YapResearch Director

Biomedical Sciences LaboratoryDefence Medical Research Institute

nmiv3@nus.edu.sg

"...a sickly child, with thin limbs and a large, pasty face surrounded by dark curly hair. He was born with defective eyesight-myopia plus anocular polyopy (multiple vision). His stomach and gall bladder gave constant trouble; he suffered from boils, rashes, and possibly from piles, for he tells us that he could never sit still for any length of time..."

Johannes Kepler(1571-1630)

• inverted image on retina• role of cornea and lens• concave & convex lenses• myope’s image in front of retina• alterations in eye shape allow distant and near vision• “near work” hypothesis: study and fine work in childhood accustoms eye to near objects, resulting in permanent finite far point.

FACE-REST DESIGNED BY KALLMANN, A GERMAN

OPTICIAN

Optics of Myopia

MYOPIAEMMETROPIA

Axial length

Corneal curvature

Refractive

Lens power

1 D = 0.32 - 0.45 mm axial length

Biometric variation

Normally distributed:– lens power– corneal power– total refraction– anterior chamber depth

Peaked, Skewed:– axial length

Emmetropization

Tron (1934): 275 eyesStenstrom (1946): 1000 eyes

Schooling and MyopiaPrevalence of myopia in 10,060 children

Thirty three Schools Grade and % of Myopiain Breslau VIII VII VI V IV III II I

5 Village schools 1 2 320 Municipal elementary 3 4 102 Middle schools 0 10 6 13 9 15 2 Girls’ high schools 1 2 7 8 6 16 12 19Holy Ghost Real 7 12 25 27 25 59Zwinger 11 21 13 23 28 29Elizabeth Gymnasium 11 17 19 31 48 65Magdelen Gymnasium 14 19 28 30 35 47

Cohn H: Hygiene of the eye. London, Simpkin, Marshall & Co, 1886

Education and Myopia

Education strongly associated with risk of myopia

Severity of myopia increased with increasing level of education

Myopia in Different Educational Groups

68% 71% 73%81%

90% 88% 86%

3% 4% 6%12%

24%18% 21%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

NFE Pri PSLE O A Dip Uni

Educational Status

Prev

alen

ce

Myopia Severe Myopia

Genetic EpidemiologyStages in identifying disease genes

RESEARCH QUESTION

Disease characteristics?

Familial clustering?

Genetic or Environmental?

Mode of inheritance?

Disease susceptibility loci?

Gene? Mutation?

METHOD/APPROACH

– Descriptive epidemiology

– Family aggregation

studies

– Twin/Adoption studies

– Segregation analysis

– Linkage analysis

– Association studies

OBJECT

Species

Population

Family

Genetic locus

Gene

Mutation

Genetic Epidemiology of Complex DiseasesLogic flow in identifying disease genes

RESEARCH QUESTIONS

Disease prevalence and features?

Familial clustering?

Genetic or Environmental?

Mode of inheritance?

Disease susceptibility loci?

Gene? Mutation?

Population Studies

Disease prevalence? Phenotypes? Risk factors?

Epidemiology of Genetic Traits and Disease

Descriptive studies of distribution– geographic differences– ethnic differences– phenotype, intermediate phenotypes

Refractive Errors in Singapore

0

500

1000

1500

2000

25002 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10

-11

-12

Spherical Equivalence (D)

No. o

f Sub

ject

s

Emmetropes: 16.2%

Mild & Moderate Myopes: 67.9%

Severe Myopes: 15.4%

15095 male subjects, mean age: 19 yrs, cohort: 1996/7

Overall Mean Sph Eq = -2.6D

0.5%

Distribution of Refractive Errors in Young Singaporean

0.05

0.15

0.25

Chinese - 2.75D

Nor: 16.2%

Mild & Moderate Myopia: 67.9%

Severe Myopia: 15.4%

Long:0.5%

Overall Median Sph Eq = -2.25D

Indian -1.13DMalay - 0.88D

17.3%

7.7%

5.9%

0.2

Freq

uenc

y

0.1

0

-12-10 -11-1 -2 -3 -4 -5 -6 -8 -9-73 2 1 0Refraction of worse eye (D)

15,095 subjects, mean age: 19 yrs, cohort: 1996/7

Age of Onset of Myopia

0

2

4

6

8

10

12

14

16

18

20

-20-18-16-14-12-10-8-6-4-20

Refractive Error at Age 19

Age

whe

n sp

ecta

cles

firs

t wor

n

Onset

Ave Onset

Myopia Complications

Peripheral Retinal Degeneration

0%10%20%30%40%50%60%70%80%90%

100%

-1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11

Refractive Error (D)

Pre

vale

nce

Macular Changes

0%10%20%30%40%50%60%70%80%90%

100%

2 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13

Refractive Error (D)

Grade VIGrade IIIGrade IIGrade I

Peripheral retinal changes in myopia (943 eyes)

Stages of macular change in myopia (1110 eyes)

Contrast Sensitivity Function

0.1

1

10

1000 1.5 3 6 12 20

Spatial Frequency (CPD)

Emmetropes+1.00 D to -1.00 D

Low Myopes-1.00 D to -6.00 D

High Myopesabove -6.00 D

Visual Acuity Trends in Young MalesSAF Pre-enlistees

73.756.7

34.4

14.7

20

32.1

11.623.3

33.5

0%

20%

40%

60%

80%

100%

1974-1984 1987-1991 1996-1997

Popu

latio

n Fr

eque

ncy

Very poor < 6

Poor 6/15 - 6

Good 6/6 - 6/

Refractive Error Trends in Males

0%20%40%60%80%

100%P

opul

atio

n Fr

eque

ncy

<-12.25 0.2% 0.3%

-8.25 to –12.00 1.5% 3.2%

-3.25 to –8.00 30.8% 37.4%

-0.75 to –3.00 28.5% 34.2%

+0.50 to –0.50 39.0% 24.9%

1993 1996-7

Familial clustering

Is there clustering of cases in families?

Family aggregation studies“Is disease more prevalent in relatives of affected than

relatives of non-affecteds?” – Relative risk, λs

– Biases: ascertainment, self-reporting (over/under), diagnostic categories, double-blind/co-morbidity studies, sampling bias

Resemblences between first degree relatives in refractive error

Reference Parent-child Sib-sib Father-mother

English 0.23 0.36 -0.12(Sorsby 66)

Alaskan Inuit 0.23 0.45 -(Young 69)

Greenland Inuit 0.07 0.25 0.03(Alsbirk 79)

Newfoundland 0.23 0.29 0.04(Bear 81)

European, Japanese 0.25 0.37 0.01(Ashton 85)

Family History

No. of Subjects who are No. of Myopic Parents Emmetropic Myopic Severely Myopic

0 47 215 106 1 or 2 20 330 234

Odds Ratio 1 3.61 5.19 P < 0.001 < 0.001

Parental History & Myopia (952 subjects)

No. of Subjects who are Myopic Siblings Emmetropic Myopic Severely Myopic

YES 34 473 304 NO 42 68 26

Odds Ratio 1 8.59 14.4 P < 0.001 < 0.001

Sibling History & Myopia (947 subjects)

Evidence of Familial Clustering of MyopiaDMRI Survey of 617 refracted subjects, 1997

20%

40%

60%

80%

100%Severe Myopia

Mild-ModerateMyopia

Non-myopia

0%No myopic

parentWith myopic

parent(s)Non-myopic sibMyopic sib(s)

Increased relative risks of myopia and severe myopia:OR = 3.6 and 5.2 (parental history)OR = 8.6 and 14.4 (sibling history)

Genetics or Environment

Is familial clustering due to common environment, inherited (genetic) susceptibility or shared cultural risk factors?

Twin studies“Is risk in identical twin of affected greater than in fraternal twin of

affected?” Concordance, discordance

Adoption studies“Is risk in biological relatives of affected adoptees greater than adopted

relatives of affected adoptees?” [Adoption bias]“Is risk in biological relatives of affected adoptees greater than biological

relatives of unaffected adoptees?”

Twin Concordance Studies

Shared Environment

Unique Environment

Genetics

DZ

MZPhenotype

sharing

0 0.5 1

Genetic sharing

Twin Studies in Myopia

MZDZ

Country Age Diag MZ DZ ConMZ ConDZ h Ref

Finland Adult 0.5D 54 55 0.80 0.51 0.58 Teikari 91

Taipei 7-23yrs QTL 49 37 0.65 0.46 0.24 Lin 87

Shanghai 7-19yrs Lo, 5D 49 37 0.82 0.58 0.61 Hu 81

Taipei 10-15yrs 0.5D 238 123 0.89 0.51 - Chen 87

Italy 3-7yrs QTL 19 20 - - 0.08-0.14 Angi 93

Next Session

Wayne Stayskal, Tampa, FL

Genetic EpidemiologyStages in identifying disease genes

RESEARCH QUESTION

Disease characteristics?

Familial clustering?

Genetic or Environmental?

Mode of inheritance?

Disease susceptibility loci?

Gene? Mutation?

METHOD/APPROACH

– Descriptive epidemiology

– Family aggregation

studies

– Twin/Adoption studies

– Segregation analysis

– Linkage analysis

– Association studies

OBJECT

Species

Population

Family

Genetic locus

Gene

Mutation

Mode of Inheritance

How is genetic susceptibility inherited?

Segregation analysis

“Is distribution of affected individuals within families consistent with a specific genetic model?”

Modes of inheritance

Single gene (Mendelian)– Autosomal

• recessive• dominant

– X-linkedSingle gene (non-Mendelian)

– Mitochondrial, ImprintedMultiple gene (complex, quantitative trait)

– digenic– oligogenic– polygenic

X-linked MyopiaBEDPartial BEDDeuteranopia

Bornholm Eye Disease:• bilateral myopia >=6D• amblyopia• optic nerve hypoplasia• RPE thinning• subnormal ERG flicke• deuteranopia

M Schwartz et al (1990) Clinical Genetics 38:281-6

An L-type calcium-channel gene mutated in incomplete X-linked congenital stationary night

blindnessTim M. Strom et al. Nature Genetics 19, 260 – 263 (1998)

Loss-of-function mutations in a calcium-channel 1-subunit gene in Xp11.23 cause incomplete X-linked

congenital stationary night blindness N. Torben Bech-Hansen et al. Nature Genetics 19, 264 – 267 (1998)

Pseudo-Mendelian Traits

Category of Adult Relatives (n) Trait (%)Fathers (249) 16.1Mothers (249) 6.0Siblings (137) 21.9Grandparents (598) 2.8Uncles / Aunts (1313) 2.1

• Overall first degree relatives 13.4• General population 0.22• Relative risk (first degree relative) 60.9• Overall second degree relatives 2.4• Relative risk (second degree relative) 10.7

“Simulation of Mendelism revisted: the recessive trait for attending medical school” P McGuffin & P Huckle 1990: Am J Hum Genet 46:994-9

Genetic Loci

Where are the genetic loci / susceptibility genes?

Linkage analysis“Is hypothetical susceptibility gene near a known genetic

marker?”– Parametric (requires known model, estimation of θ,

penetrance): extended pedigree– Nonparametric: Affected relative pair analysis (eg. sib-pair)

Approaches to Linkage and Association

Linkage AnalysisParametric AnalysisNon-parametric Analysis

Affected relative pairs

Linkage Disequilibrium / Association AnalysisCase-controlFamily-based association

Genetic Linkage Analysis

c/da/b

Classical Linkage Sib-pair Linkage

•120 concordant Sib Pairs•SAF and SERI•top 10 percentile•Chinese

Human Genetics Approaches

Candidate Gene“Hypothesis”

Genome Wide“Discovery”

a/b c/d

a/c

Case Control Association

Family Based Association

Sib-pair Linkage

n = 95 severe myopesn = 120 concordant sib pairs

Tools for Linkage and Association Analysis

MarkersShort Tandem Repeats / MicrosatellitesMinisatellites / Variable Number of Tandem RepeatsSingle Nucleotide Polymorphisms

Maps

Genotyping Technologies

CH

RO

MO

SOM

E L

INK

AG

E M

AP

OF

TH

E

OX

FOR

D M

ICR

OSA

TE

LL

ITE

SE

T (R

eed)

Non-Parametric Linkage Analysis

Affected Relative PairsSib Pair - concordant

discordant

c/da/b

Alleles IBDa/c 0 b/da/c 1 b/ca/c 1 a/da/c 2 a/c

Alleles Identical by DescentSib-pairs sharing 0 1 2No linkage 25% 50% 25%Linkage eg 10% 55% 35%

Non-Parametric Linkage Analysis

without parental info

Alleles IBSa/c 0 b/da/c 1 b/ca/c 1 a/da/c 2 a/c

Alleles Identical by State

Mapping Complex Traits by Genome Wide Linkage Analysis

Type I diabetesType II diabetesMultiple sclerosisRheumatoid arthritisCrohn’s diseaseEssential hypertensionCoronary artery diseaseAsthmaAlcoholismSchizophrenia

Many others

cM

11.32

11.31

11.2

11.17.6cM

D18S1140

“Evidence that a locus for familial high myopia maps to chromosome 18p.”Young TL et al. (1998) Am J Hum Genet 63:109-19.

D18S591.5

D18S476D18S11460.1

4.5

D18S4811.4

D18S63D18S11380.1

0.7 D18S52

9.4

D18S62

18.6

D18S11504.1

D18S1116Idiogram of Chromosome 18

Genethon Genetic Map

D12S1052D12S1684D12S1708D12S81D12S1710D12S351

D12S393

D12S1588

D12S318

30.1cM

Idiogram of Chromosome 12

Genethon Genetic Map

D12S327D12S1716

24.324.224.12322

21

15141312

11.2

12

13

D12S1706D12S346D12S1671 “A second locus for familial

high myopia maps to chromosome 12q.”Young TL et al. (1998) Am J Hum Genet 63:1419-24

D12S306D12S1607PAH

D12S1074D12S360D12S78D12S338D12S1075D12S317D12S1605D12S2070

Sib –pair IBD analysis (MLS)

Data not available

Sib –pair IBD analysis

Data not available

Multipoint non-parametric linkage analysis (NPL)

NPL score: 2.23

TDT analysis

Data not available

Population-optimal marker panelsComparison of established panels among

Caucasian, Japanese and Chinese

Wu Hui Min / Tan Ene ChooRita Yong, Selena Tan, Joyce Chang,

Linda Gan, Eric Yap

Whole genome STR marker in 200 unrelated Chinese individuals

0.000.100.200.300.400.500.600.700.800.901.00

0 5 10 15 20 25Number of Alleles

Het

eroz

ygos

ity

Heterozygosity of STR markers in 3 populations

0

10

20

30

40

50

60

<0.3

0

0.31

-0.4

0

0.41

- 0.

50

0.51

- 0.

60

0.61

- 0.

70

0.71

- 0.

80

0.81

- 0.

90

> 0.

90

Heterozygosity

Freq

uenc

y (%

)

Caucasian Japanese Chinese

Caucasian 90.8%Japanese 63.7%Chinese 63.6%

h > 0.7

Heterozygosity of STR markers in 3 populations

0

5

10

15

20

25

30

-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45

Difference in Heterozygosity

Freq

uenc

y (%

)

Chinese vs Caucasians

Chinese vs Japanese

Less informative in ChineseMore informative in Chinese

• 285 STR marker panel (Reed et al.)– Oxford panel selected from Genethon

• Median heterozygosity 0.72 (Tan/Wu, Luo)

• h independent of sample size – Simulation: 10<n<200 for 2-27 alleles

• Propose using 192 STR with h >0.7, covering 84% of genome at 20cM

Mining for polymorphic STR useful for high resolution genetic mapping

Liu Hai Feng, Teow Loo NinWu Hui Min, Linda Gan, Ng Sock Hoon,

Eric Yap

Genome/Contig sequence

Identify tandem repeats

parser Tandem Repeat Finder

Wet lab validation and use

$$$

Map of Chromosome 12q21(83 Mb to 95 Mb)

Repeats 1 2 3 4 5 6 more total

Number 12 50 3 24 8 7 112 216

1 cM

Predicted dinucleotide repeats in chromosome 12q (85 Mb - 95 Mb) by TRF

No. of contigs: 18 (build 29)

Total length: 10,468 kb

No. of DTR: 789 (Density : 0.075 per kb or 1 per 13.3kb)

Genome/Contig sequence

Identify tandem repeats

parser Tandem Repeat Finder

Predict highly polymorphic STR

Machine learning MLAP

Wet lab validation and use

Machine Learning for Predicting Polymorphisms

• Learning and test set– Genethon dinucleotide markers

• Highly polymorphic h>0.8• Lowly polymorphic h<0.5

• Parameters– Mechanism: strand slippage during replication

Machine learning algorithm for prediction of high-polymorphic DTRs

Data not available

Characteristics of MLAP Predictions

304

454

31

NP P HP

The no. of predicted polymorphism of candidate DTRs by MLAP, where “NP” represents non-polymorphic(Het < 0.5), “HP” represents highly polymorphic (Het > 0.8), and “P” represents those with Het between 0.5 and 0.8.

H <

0.10

0.10

£ H

< 0

.20

0.20

£ H

< 0

.30

0.30

£ H

< 0

.40

0.40

£ H

< 0

.50

0.50

£ H

< 0

.60

0.60

£ H

< 0

.70

0.70

£ H

< 0

.80

0.80

£ H

< 0

.90

0.90

£ H

< 1

.00

AT

C A0

2

4

6

8

10

12

Heterozygosity

Type of repeat and polymorphism

AT

GA

CA

H <

0.10

0.10

£ H

< 0

.20

0.20

£ H

< 0

.30

0.30

£ H

< 0

.40

0.40

£ H

< 0

.50

0.50

£ H

< 0

.60

0.60

£ H

< 0

.70

0.70

£ H

< 0

.80

0.80

£ H

< 0

.90

0.90

£ H

< 1

.00

INTRA

012345678

Heterozygosity

INTRA

INTER

Position and polymorphism

Validation of DTR polymorphisms

Heterozygosity of HP and LP DTRs

0

2

4

6

8

10

12

14

0 ≤

Η <

0.1

0

0.10

≤ Η

< 0

.20

0.20

≤ Η

< 0

.30

0.30

≤ Η

< 0

.40

0.40

≤ Η

< 0

.50

0.50

≤ Η

< 0

.60

0.60

≤ Η

< 0

.70

0.70

≤ Η

< 0

.80

0.80

≤ Η

< 0

.90

0.90

≤ Η

< 1

.00

Heterozygosity

Freq

uenc

y

LP DTRs

HP DTRs

20 HP and 9 NP markers were selected for genotyping in 24 unrelated Chinese individuals. Frequency of observed heterozygosity for each marker in the 2 groups is shown. The prediction accuracies were 95% and 33% for HP and NP group respectively.

Gene and Mutation

What gene and mutations are associated with diseas

Disease-genotype association, linkage dysequilibrium“Do affected individuals have certain allele/genotype more often

than by chance?”– Population-based allelic association– Family-based allelic association

Mutation analysis“Are there functional mutations that account for phenotype?”

Gene Association Studies

a/b c/d

a/c

Case Control Association

Family Based Association

Population Admixture

Allele m

Allele M

Differing allelic frequencies and disease prevalences in two subpopulations, with no biological association –> Apparent associationIf both subpopulations mate randomly and completely (panmixia), then population is homogeneous and admixture is no longer significant.To overcome artifacts:

– use homogeneous populations– replicate study in several

populations– use meiotic (family-based)

association studies

Population I Population II

HEALTHY HEALTHYDISEASE

Family-Based Association

Types of analyses:Haplotype relative risk (HRR) Rubinstein& FalkAffected family-based controls (AFBAC) ThomsonTransmission distortion test (TDT) Spielman

a/b c/d

a/c

HRR eg.Alleles a b c dtransmitted 1 0 1 0not transmitted 0 1 0 1

“Are alleles a and c transmitted more frequently in affected than alleles b and d?”

Trabecular Meshwork Inducible Glucocrticoid Receptor(TIGR) or Myocilin Gene

NGA17

NGA19Exon 1 Exon 3Exon 2

-224

C/T

-103 to –99

TATA boxNGA17

NGA19Exon 1 Exon 3Exon 2

-224

C/T

-103 to –99

TATA box

A A A T A A C C T T CC A/G G A A G T C T G T T T G G

A A A T A A C C T T C C A G A A G T C T G T T T G G A

A A A A T A A C C T T C C G G A A G T C T G T T T G G A

A A A T A A C C T T CC A/G G A A G T C T G T T T G GA A A T A A C C T T CC A/G G A A G T C T G T T T G GA A A T A A C C T T CC A/G G A A G T C T G T T T G G

A A A T A A C C T T C C A G A A G T C T G T T T G G A

A A A A T A A C C T T C C G G A A G T C T G T T T G G A

A A A T A A C C T T C C A G A A G T C T G T T T G G AA A A T A A C C T T C C A G A A G T C T G T T T G G A

A A A A T A A C C T T C C G G A A G T C T G T T T G G AA A A A T A A C C T T C C G G A A G T C T G T T T G G A

100

bp

Mar

ker

T/T

C/C T/

C

T/C

T/C

294 bp223 bp

100

bp

Mar

ker

T/T

C/C T/

C

T/C

T/C

100

bp

Mar

ker

T/T

C/C

100

bp

Mar

ker

T/T

C/C T/

C

T/C

T/C

294 bp223 bp294 bp223 bp

Novel SNP in TIGR 5’UTR

Population No of chromosomes

Allele frequency

Heterozygosity observed

Chinese 64 T1: 0.59 T2: 0.41

0.50

Malays 64 T1: 0.59 T2: 0.41

0.50

Indians 64 T1: 0.87 T2: 0.13

0.19

Caucasian 20 T1: 0.75 T2: 0.25

0.30

African-American

20 T1: 0.45 T2: 0.55

0.70

Middle Eastern 20 T1: 0.75 T2: 0.25

0.50

American-Indians

20 T1: 0.80 T2: 0.20

0.44

Mexican 20 T1: 0.95 T2: 0.05

0.10

Puerto Rican 20 T1: 0.85 T2: 0.15

0.11

Data for TDT Analysis

Age Gender Refraction (Mean, SD)

• First sample set 16-43 M:46 -6.5 to –16.75D91 cases (21.5,1) F:45 (-11.25, 2.15)

• Second sample 5-15 M:75 -1.5 to –14.85D 129 cases (10.3, F:54 (-5.89, 3.33)

5.4)

Markers in TIGR Gene

NGA17

NGA19Exon 1 Exon 3Exon 2

-224

C/T

-103 to –99

TATA boxNGA17

NGA19Exon 1 Exon 3Exon 2

-224

C/T

-103 to –99

TATA box

18.6kb D’=0.38

0.1kbD’=0.35

18.7kb D’=0.17 N >= 200 individuals

Family Association analysis of TIGR Gene

Single locus TDT analysis

ns

p < 0.001

p = 0.002

0

10

20

30

40

D1S210 D1S2815 NGA17 TIGR NGA19

Markers

Chi-s

quar

e

X2 (Sum)X2 (Max)

TDT analysis of the 3 markers of the MYOC gene in myopia families.

MarkersNo of Allele Het (%) X 2

sum

Allele (%) TR NT X 2

OR (95% CI)

NGA19 7 60.5 27.89* 122 (1.2) 0 2 2124

(23.3) 21 43 7.56126 (0.6) 3 0 3128

(65.7) 57 30 8.38†3.4 (1.84,

6.13)130 (5.2) 6 8 0.29132 (2.3) 0 6 6134 (1.7) 4 2 0.67

*p = 0.001, †p = 0.013

a. First family set (44 families):

TDT analysis of the 3 markers of the MYOC gene in myopia families.

b. Second family set (60 families):

MarkersNo of Allele Het (%) X 2

sum

Allele (%) TR NT X 2

OR (95% CI)

NGA19 4 71.9 11.32* 124 (27.1) 38 47 0.95128

(69.5) 55 36 3.972.2 (1.25,

3.39)130 (3.0) 3 12 5.4132 (0.4) 0 1 1

*p = 0.04,

TDT analysis of the 3 markers of the MYOC gene in myopia families.

c. Combined family set (104 families):

MarkersNo of Allele Het (%) X 2

sum

Allele (%) TR NT X 2

OR (95% CI)

NGA19 7 53.4 35.18* 122 (0.5) 0 2 2124

(25.5) 59 90 6.45126 (0.2) 3 0 3128

(67.9) 112 66

11.89**2.7 (1.80,

4.13)130 (3.9) 9 20 4.17132 (1.2) 0 7 7134 (0.7) 4 2 0.67

* p < 0.001, ** p = 0.002

Family Association analysis of TIGR Gene

Multi-locus TDT analysis

Haplotypes %

TR (Obs)

TR (Exp)

X2

(1df ) P

(2sided) **TIGR-NGA19

T1 128 30.5 113.74 95.38 9.88 0.002 NGA17-NGA19 215 128 19.5 70.63 57.78 7.31 0.007

NGA17-TIGR NGA19 215 T1 128 19.5 66.5 53.23 8.37 0.004

* Global p < 0.05, ** Global p = 0.005

*

*

Significant association of allele 128 of NGA19 and severe myopia

Summary & Conclusions

Locally developed capability:– facilities for high

throughput genotyping capability

– unique expertise in genetic epidemiology for disease gene hunting

Application to other dis:– SLE, Hypertension– Pb poisoning, Diabetic

nephropathy

Myopia is a complex (heterogeneous) genetic disease

Evidence for a novel gene on chromosome 12 predisposing to myopia discovered

Replicated allelic and haplotypic association to TIGR gene

Genetics Approaches

Positional Cloning / Linkage

•Discovery-based, systematic*•Genome-wide*•Mendelian*•Study relatives – extended or nuclear families*•Large pedigrees with multiple affecteds ideal*•Highly informative markers (Microsatellites)*

Candidate Gene / Association (Linkage Dysequilibrium)•Hypothesis-driven, intuitive, pathways or models*•Not genome-wide*•Complex diseases*•Requires individuals, small families*•Isolated homogeneous population ideal*•Highly abundant markers (SNPs)*

* With Exceptions

Research Team

Myopia & Human Genetics GroupDMRI/SERI