Molecular Genetics of Psoriasis

.................................................................................................................8 INTRODUCTION......................................................................................................10 REVIEW OF THE LITERATURE .........................................................................12 1. Mapping of complex diseases ..............................................................................12 1.1. Difficulties in mapping complex diseases .....................................................12 1.2. Allelic structure of complex diseases ............................................................12 1.3. Single nucleotide polymorphisms (SNPs) .....................................................14 1.4. Association studies........................................................................................14 1.5. Genome-wide linkage analysis .....................................................................16 1.6. Linkage disequilibrium mapping ..................................................................17 1.7. Use of population isolates.............................................................................19 2. Clinical features of psoriasis ...............................................................................20 2.1. Clinical characteristics and related diseases ...............................................20 2.2. Prevalence.....................................................................................................22 2.3. Age of onset...................................................................................................22 3. Pathogenesis of psoriasis.....................................................................................23 3.1. Keratinocytes ................................................................................................24 3.2. Inflammatory cells ........................................................................................24 3.3. Cytokines.......................................................................................................25 3.4. Pathogenetic models .....................................................................................26 4. Genetics of psoriasis ............................................................................................27 4.1. Family and twin studies ................................................................................27 4.2. Inheritance models........................................................................................28 4.3. The HLA association.....................................................................................30 4.3.1. The Major Histocompatibility Complex.................................................30 4.3.2. The HLA association with psoriasis ......................................................31 4.4. Linkage analyses ...........................................................................................33 5. The PSORS1 locus in the MHC region ................................................................37 5.1. Refinement of PSORS1..................................................................................37 5.2. Candidate genes at PSORS1.........................................................................38 AIMS OF THE STUDY.............................................................................................41 MATERIALS AND METHODS ..............................................................................42 1. Study subjects.......................................................................................................42 1.1. Finnish psoriasis families .............................................................................42 1.2. Foreign psoriasis families.............................................................................42 1.3. Guttate psoriasis and PPP patients ..............................................................43 1.4. Skin biopsies..................................................................................................43 2. Reverse Transcriptase (RT)-PCR ........................................................................43 3. PCR amplification and direct sequencing ...........................................................43 4. SSCP analysis ......................................................................................................44 5. In situ hybridization .............................................................................................44 6. Genotyping of SNPs .............................................................................................44 7. Production of antibodies......................................................................................45 8. Western blotting ...................................................................................................45 9. Immunohistochemistry .........................................................................................46 10. Genotyping of microsatellite markers................................................................46 11. Statistical analyses.............................................................................................46 11.1. Linkage analysis..........................................................................................46 11.2. Haplotype association analysis...................................................................47 11.3. Transmission Disequilibrium Test (TDT) ...................................................47 11.4. Other tests for allele association ................................................................48 11.5. Linkage disequilibrium tests .......................................................................48 RESULTS AND DISCUSSION ................................................................................49 1. Characterization of the HCR (Pg8) gene structure (I, II) ...................................49 2. Detection and screening of HCR polymorphisms (I, III) .....................................49 2.1. Nomenclature of the HCR SNPs (I-IV) .........................................................50 3. Case-control association analysis of HCR SNPs (I)............................................50 4. Association and haplotype analysis of PSORS1 susceptibility alleles (II) ..........52 5. PSORS1 allele associations in GP and PPP (III)................................................54 5.1. GP shares genetic background with PV .......................................................54 5.2. PPP is not associated with PSORS1.............................................................56 6. HCR mRNA is overexpressed in psoriatic skin (I)...............................................56 7. Altered structure and expression of HCR protein in psoriasis (II, III)................57 8. HCR gene orthologues in primates (unpublished)...............................................58 9. Defining the PSORS1 risk gene ...........................................................................58 10. A minor locus for psoriasis on 18p in PSORS1 negative families (IV) .............60 CONCLUSIONS AND FUTURE PROSPECTS.....................................................63 ACKNOWLEDGEMENTS ......................................................................................65 REFERENCES...........................................................................................................67 ORIGINAL COMMUNICATIONS.........................................................................80