1. Discovering Disease Genes- The Example of Schizophrenia
Pippa Thomson, Medical Genetics Section, Dept of Medical Sciences, MMC, University of Edinburgh.

2. Importance of the illness
Severe psychiatric
Affects ~1% of the population
One of the top 10 causes of disability worldwide
Economic cost (23% Drug, 14% Hospital)
Pharmacological rationale for treatment weak or absent
1/3rd patients unresponsive or experience unacceptable side effects
Strong genetic component
concordance rate between identical twins of 60%

3. Schizophrenia
Positive symptoms: visual & auditory hallucinations, delusions, incoherent speech

4. Schizophrenia
Negative symptoms: withdrawal & isolation, impaired attention & blunted emotions

5. Altered brain structure & function

6. High Heels Cause Schizophrenia and 6 Other Outlandish Medical Theories
2. High-heeled shoes cause schizophrenia. You have to wonder where some medical theories originate. Why did Swedish scientist Jarl Flensmark decide to study a connection between heeled shoes and the incidence of schizophrenia? The world may never know. But his initial research seems sound, and he has connected certain brain activity with stimulation of certain points on the feet. The spread of schizophrenia around the globe has closely followed the spread of availability of heeled shoes. Is it an eerie coincidence or a real cause for concern? Look out, men - this theory applies not only to stilettos, but to any shoe with a heel.
remedicated.com

7. Relative risk of developing Schizophrenia
Environment !

8. Benefits of gene identification
Understand aetiology
Improved drug development & testing
Development of definitive diagnostic tests
Understanding of interaction with non-genetic risk factors
Insight into normal brain development & function
Kraepelin, 1896
“As we do not know what causes the illness there cannot be a rational treatment”

9. Allelic architecture and mapping strategy
Magnitude of effect
Frequency in population
Family-based
linkage studies
Association studies in populations
Unlikely to exist
Fnct. Studies

10. Locus Identification-problems
Uncertainty in diagnostic boundaries
Non-Mendelian inheritance
Variable age of onset
Genetic heterogeneity
Many different genes can cause the illness
1% risk world wide
phenotypic variation
Oligogenic/polygenic causation
More than one mutant gene required to produce phenotype

11. Locus identification- reducing the problems
Single large families
Avoid bilineal descent
rigorous interviews
family history
Reduce genetic heterogeneity
Significant LOD score = gene of major effect
Reduce uncertainty of diagnosis
classify minor diagnoses as unaffected
>1 category of affected phenotype

12. Linkage Analysis
Marker analysis in multiply affected family or families
Look for co-segregation of a particular allele with phenotype
Results expressed as a LOD score (Significant at > 3)
= log (likelihood of data, if locus & disease are linked)
(likelihood of data, if locus & disease are not linked)
Generally a large region is identified

13. A balanced t(1;11)(q42;q14) translocation
der1
der11 11 1

14. translocation increases risk by 50-fold
t(1;11) co-segregates with major mental illness
translocation increases risk by 50-fold ?
Translocation co-segregates with psychiatric illness in this family
Range of diagnoses
Arrows mark translocation
All major diagnoses co-occur with translocation
schizophrenia
(1;11)(q42;q14) translocation
recurrent major depression
unaffected
bipolar affective disorder
minor diagnosis

15. Controls Schizophrenics
100’s Individuals = 1% Schizophrenia
100’s Individuals = 100% Schizophrenia
Controls
Schizophrenics
Genetic association studies seek to relate variation in human DNA sequence with a disease or trait
Association method provides greater power to detect common genetic variants conferring susceptibility to complex phenotypes
Estimates population attributable risk (effect size)
Controls should match cases and be a representative sample of the population.
For final bullet point
Though the case-control design may be simple, interpreting the results of these genetic association studies has been far less straightforward 15

16. Case-control association studiesG C
Comparison of frequencies of polymorphisms between populations of cases and controls (usually a simple chi-square test or logistic regression)
Polymorphism studied can be directly responsible for the defect  frequency of cases >>> controls
Polymorphism studied can be in linkage disequilibrium with the mutation responsible for the disease  %T cases >> controls
Association studies can be conducted for candidate genes, or through a whole region or across the whole genome (WTCCC)
In complex disease the results of case-control association studies may not be clear cut, as some controls will also carry the associated allele, and some cases may be linked to genes in other regions. p Mb

17. International HapMap project
SNPs are genotyped in parent-offspring trios, initially in CEPH trios.
This can be used to identify SNPs that co-segregate (i.e. are in linkage disequilibrium) versus those that segregate independently.
A subset of SNPs can therefore be chosen that best represent the genetic diversity in a region/gene, reducing the costs of genotyping.
Summary of genotyped SNPs:
Populations CEU CHB+JPT YRI
Total Non-Redundant 3,204, ,244,897 3,150,433

18. Linkage Disequilibrium
Region of interest
HapMap genotyped SNPs
Known SNPs*
Known genes in the regions
In the linkage disequilibrium diagram, the pairwise LD between all the markers in the selected region is shown. Red indicates complete LD, pink intermediate, white independence, grey a lack of recombination event leading to uncertainty i.e. where one of the SNPs has a rare allele.
Linkage Disequilibrium
(LD) *

19. Tagging SNP selection
Proportion of haplotype diversity explained : SNPs %
SNPs %

20. Genetic evidence implicating DISC1 in psychiatric illness
LOD=2, BRITAIN & ICELAND (Curtis et al 2003)
D1S251
LOD=1, TAIWAN (Hwu et al 2003)
SCZ
BPAD
LOD=7.1, SCOTLAND
SCZ & BPAD & MDD
TRANSLOCATION
p=0.0044, p=0.0016
SCOTLAND
LOD=3.21, FINLAND (Ekelund et al 2001)
SCZ
D1S2709
SCZ, BPAD
HAPLOTYPE 1 2 3 4 5 6 7 8 9 10 11 12 13
DISC1
HAPLOTYPE
p= , FINLAND (Hennah et al 2003)
SCZ & SCZAFF
DISC2
p= , North-America (Hodgkinson et al 2004) rs
SCZAFF

21. Genes for Schizophrenia ?
>130 genes implicated
Table 1. Summary of current evidence supporting several of the more promising genes implicated in schizophrenia, bipolar disorder, and mixed bipolar-psychosis phenotypes
Craddock et al., SCZ Bulletin, 2006

22. protein-protein interactions
DISC1 interactome
protein-protein interactions
Chris Carter,

23. Effects of altered DISC1 on gene expression
ENU generated mouse mutants
Two independent lines with missense mutations in DISC1 exon 2
Q31L (Glutamine-Leucine)
Q- hydrophillic; L – hydrophobic
L100P (Leucine-Proline)
Predicted to cause transition in polypeptide chain direction
Normal levels of DISC1 protein in brain
L100P line models schizophrenia; Q31L, depression
Clapcote et al., Neuron May 3;54(3):

24. Effects of Altered DISC1 on Behaviour (How do you know if a mouse is schizophrenic?)
Schizophrenia
Depression

25. Effects of altered DISC1 on gene expression
Samples collected and microarray study ongoing
Mutated lines vs background strain (C57/BL6)
47,000 transcripts
Hippocampus
Adult and embryonic stage- Microarray
Confirmation/Investigation of changes
Series of embryonic; postnatal and adult stages
Drug treated adult mice
Detect disrupted pathways

26. Whole genome sequencing
Resequencing, SNP detection, genome comparisons, gene expression, transcription factor studies, small RNA analysis
Individual genomes – All SNPs in each individual
Currently :
Using the Illumina 1G to sequence genes in the DISC1 pathway.
Total sequence read 3.5megabases in 1200 individuals
Identify coding and non-coding polymorphisms
Mutation detection
Detection of variants in conserved regions
Detection of variants affecting binding of transcription factors

27. Psychiatric Genetics- Unanswered Questions
How many susceptibility genes are there? What is their function? Is function conserved across species? Can we relate gene (dys)function to mental (dis)order? Do gene variants predict risk, course, outcome and response to treatment? Will gene discovery lead to drug discovery? How do genes and environment interact? How and when will the patient benefit?

28. Acknowledgements DISC1 Medical Genetics Kirsty Millar
Shaun Mackie
Fumiaki Ogawa
Jennifer Chubb
Becky Carlyle
Nick Bradshaw
Sheila Christie
Steve Clapcote
Kathy Evans
Sarah Brown
William Hennah
Medical Genetics
Prof David Porteous
Prof Douglas Blackwood
Walter Muir
Ben Pickard
Other collaborators
DISC1 Consortium
Wellcome Trust CRF
Illumina, San Diego
Cold Spring Harbor laboratories