Dr. Karlsen's abstracts from the AASLD 2007 Meeting

[Guest guest]

Dear All;

Because Dr. Karlsen is the winner of the 2007 PSC Partners

Seeking a Cure award at the AASLD 2007 meeting this November, I

thought I would share with you these two abstracts that he is

presenting at this meeting (a sneak peak). Both abstracts reveal

significant new insights concerning the genetic basis of PSC:

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Variation in the MDR3 gene influences disease progression in PSC

patients and disease susceptibility in epistatic interaction with a

polymorphism in the OST-alpha gene.

E. Melum 1, 2; K. M. Boberg 1; A. e 3; A. Bergquist 4; J. Hampe

5; S. Schreiber 3; B. A. Lie 2; E. Schrumpf 1; T. H. Karlsen 1, 2

1. Medical Department, Rikshospitalet-Radiumhospitalet Medical

Center, Oslo, Norway.

2. Institute of Immunology, Rikshospitalet-Radiumhospitalet Medical

Center, Oslo, Norway.

3. Institute for Clinical Molecular Biology, Christian-Albrechts

University, Kiel, Germany.

4. Department of Gastroenterology and Hepatology, Karolinska

University Hospital, Huddinge, Stockholm, Sweden.

5. 1st Department of Medicine, Christian-Albrechts University, Kiel,

Germany.

Background and aims:

The multi drug resistance 3 gene (MDR3) on chromosome 7q21 encodes a

phospholipid transporter of importance to cholangiocyte membrane

integrity and bile solubility (ABCB4; ATP-binding cassette, sub-

family B, member 4). Knockout mice of the murine MDR3 analogue (mdr2)

develop a cholestatic disease resembling primary sclerosing

cholangitis (PSC) in humans. The aim of the present study was to

investigate the influence of polymorphisms in the MDR3 gene on

disease susceptibility and progression in PSC. Genes encoding other

transport proteins in the biliary tract were studied simultaneously

to evaluate gene-gene interaction (epistasis) on disease

susceptibility.

Methods:

Single nucleotide polymorphisms (SNPs) covering 10 genes encoding

transport proteins for a variety of bile constituents (MDR3, BSEP,

FIC1, MRP2, MRP3, MRP4, ASBT, I-BABP, OST-alpha and OST-beta) were

genotyped with SNPlex® technology in 365 Scandinavian PSC patients

and 368 healthy controls. Association testing was performed with the

Chi-squared test, and epistatic effects were evaluated using logistic

regression. Survival was defined as the time from the diagnostic

cholangiography to the combined end-point of death or liver

transplantation. Effects from genotypes on disease progression were

evaluated with regressions.

Results:

No associations with PSC susceptibility were seen for any of the

individual SNPs. An epistatic interaction between the MDR3 SNP

rs8187799 and the OST-alpha SNP rs11185519 affected PSC risk (p=6.6 x

10-6). This effect was robust to correction for multiple comparisons

using Bonferroni (pc=0.01). Two MDR3 SNPs in linkage disequilibrium

significantly influenced survival: rs1202283 (AA vs. AG+GG: median

9.8 vs. 14.4 years) and rs4148809 (AA vs. AG+GG: median 9.6 vs. 15.4

years). In regressions, patients homozygous for the A allele at

rs1202283 and rs4148809 had an increased risk of death or liver

transplantation (hazard ratio (HR)=1.6, p=0.006 and HR=1.7, p=0.002,

respectively). To rule out that this effect was caused by a higher

age at diagnosis of PSC or concomitant cholangiocarcinoma, patients

with cholangiocarcinoma were excluded and age adjusted

regressions were performed, with no change in result (rs1202283

HR=1.7, p=0.007 and rs4148809 HR=1.8, p=0.002).

Conclusions:

Although no associations with any individual SNPs were seen, our

present data provide interesting evidence that polymorphisms in the

MDR3 gene influence disease progression in PSC patients, and

susceptibility to develop PSC in epistatic interaction with a

polymorphism in the OST-alpha gene.

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HLA association in primary sclerosing cholangitis: Detection and

finemapping of an HLA independent signal in the complement gene

cluster.

T. H. Karlsen 1, 2; P. Croucher 3, 4; J. Hampe 4, 5; A. e 4; E.

Schrumpf 1; A. Bergquist 6; E. Thorsby 2; B. A. Lie 2; K. M. Boberg

1; S. Schreiber 4

1. Medical Department, Rikshospitalet-Radiumhospitalet Medical

Center, Oslo, Norway.

2. Institute of Immunology, Rikshospitalet-Radiumhospitalet Medical

Center, Oslo, Norway.

3. Institute of Medical Informatics and Statistics, Christian-

Albrechts-University, Kiel, Germany.

4. Institute for Clinical Molecular Biology, Christian-Albrechts-

University, Kiel, Germany.

5. Department of General Internal Medicine, University Hospital

Schleswig-Holstein, Kiel, Germany.

6. Department of Gastroenterology and Hepatology, Karolinska

University Hospital, Stockholm, Sweden.

Background: An association between the risk of developing primary

sclerosing cholangitis (PSC) and genetic variants within the HLA

complex on chromosome 6p21 was detected 25 years ago. This genetic

region contains more than 250 closely linked genes, and pinpointing

the genetic variants of relevance to PSC has proven extremely

difficult. In an attempt to further refine the HLA association in

PSC, systematic mapping of the entire HLA complex was performed in a

large cohort of Scandinavian PSC patients.

Materials and methods: 365 PSC patients and 368 healthy controls were

genotyped for all classical HLA loci (HLA-A, -B, -C, DRB1, DRB3 and

DQB1) using a sequencing based approach. A two-stage screen using

single nucleotide polymorphism (SNP) markers was subsequently

performed. In stage one, 420 SNPs were successfully genotyped with

SNPlex® technology. Dissection of the association signals was

performed using established statistical packages as well as novel

statistical approaches. In stage two, saturation of a distinct risk

region using additional 130 SNPs was performed to localize causative

variants.

Results: The SNP screen revealed the presence of a wide and complex

association signal blurred by a strong-LD haplotype that may harbor

several variants strongly associated with PSC, e.g. at HLA-B (odds

ratio [OR] HLA-B*08 = 3.5, 95% CI [2.6-4.5], p<10-16) and MICA (OR

rs2523495_A = 3.5, 95% CI [2.7, 4.5], p<10-16), which have also been

reported in previous studies. When case haplotypes were proactively

matched with randomly drawn control haplotypes at markers defining

this strong-LD haplotype (i.e. HLA-B*08 and DRB1*0301), a distinct

association signal became evident at the complement factor gene

cluster within the central HLA class III region. Maximum association

in this risk region was observed for a common allele at an intronic

SNP (69% vs. 48%, OR=2.5, 95% CI [2.0, 3.1], p=10-16). Interestingly,

this allele maps to all known HLA risk haplotypes in PSC (i.e. DR3,

DR6 and DR2), while previously reported protective HLA haplotypes in

PSC (i.e. DR4, DR7 and DR11) predominantly carry the opposite allele

at this position.

Conclusion: The present dataset provides an extensive insight into

the complexity of the HLA association in PSC. Multiple risk variants

are likely to exist, some of which have been previously reported in

other autoimmune diseases (e.g. at HLA-B and MICA), and others which

are PSC-specific. Novel alignment strategies with known risk and non-

risk HLA haplotypes in PSC helped to dissect a distinct risk locus

for PSC in the central HLA class III region. Ongoing analyses aim to

identify the exact susceptibility gene within this region.

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Best regards,

Dave

(father of (23); PSC 07/03; UC 08/03)