Bjornsson, Einar Stefan

76 Background: The prevalence of Lynch syndrome in Iceland is the highest described so far or 1:226 with three founder mutations, one in MSH6 and two in PMS2, and was first reported in 2017. Lynch syndrome predisposes carriers to colorectal cancer and metachronous primaries. Most data on metachronous colorectal cancer reflects on MLH1 and MSH2 carriers and is not well described in MSH6 and PMS2 carriers. The purpose of this study was to examine the cumulative incidence of metachronous colorectal cancer in Icelandic Lynch syndrome carriers diagnosed with colorectal cancer from 1955-2017. Methods: This retrospective study included all individuals with pathogenic variants in mismatch repair genes identified in a nationwide genotype database and a colorectal cancer diagnosis in the Icelandic Cancer Registry from 1955-2017. DeCODE genetics has collected extensive genotypic information on the Icelandic population sequencing the whole genomes of 49,708 Icelanders and imputing genotypes into 116,573 Icelanders whose DNA had been genotyped with SNP chips. Cancer information was obtained from patient charts and cause of death obtained from the Cause of Death Register. All polyp pathology was accessed in the pathology registry and reassessed by two pathologists. Results: A total of 65 individuals developed colorectal cancer during the study period with 34 (52.3%) PMS2 carriers and 25 (38.5%) MSH6 carriers. The cumulative incidence of metachronous colorectal cancer was low or one case (1.5%) in an MSH2 carrier with a median follow-up time of 58 months (Q1 8.0, Q3 167.0, range 0-365 months) in the cohort. Only two (3.1%) individuals, one with MSH2 and one with MSH6 pathogenic variants, underwent a total colectomy. Median age at first colorectal cancer diagnosis was 63 years (Q1 54.0, Q3 72.5, range 28-94). Thirty-one (47.7%) individuals had polyps resected during the study period with adenomas (67.1%) being the most common. Significantly more MSH6 carriers had a history of advanced adenomas as compared to PMS2 carriers (36.0 % vs 11.8%, p = 0.026). Five-year colorectal cancer survival was 81.4% for PMS2 carriers and 71.5% for MSH6 carriers. Conclusions: The incidence of metachronous colorectal cancer was zero in Lynch syndrome carriers with MSH6 or PMS2 pathogenic variants from 1955-2017 despite these individuals not undergoing rigorous Lynch syndrome screening. This would support performing segmental colectomies and following European screening guidelines for MSH6 and PMS2 carriers in Iceland.

Objective Primary sclerosing cholangitis (PSC) is a genetically complex, inflammatory bile duct disease of largely unknown aetiology often leading to liver transplantation or death. Little is known about the genetic contribution to the severity and progression of PSC. The aim of this study is to identify genetic variants associated with PSC disease progression and development of complications. Design We collected standardised PSC subphenotypes in a large cohort of 3402 patients with PSC. After quality control, we combined 130 422 single nucleotide polymorphisms of all patients—obtained using the Illumina immunochip—with their disease subphenotypes. Using logistic regression and Cox proportional hazards models, we identified genetic variants associated with binary and time-to-event PSC subphenotypes. Results We identified genetic variant rs853974 to be associated with liver transplant-free survival (p=6.07×10–9). Kaplan-Meier survival analysis showed a 50.9% (95% CI 41.5% to 59.5%) transplant-free survival for homozygous AA allele carriers of rs853974 compared with 72.8% (95% CI 69.6% to 75.7%) for GG carriers at 10 years after PSC diagnosis. For the candidate gene in the region, RSPO3, we demonstrated expression in key liver-resident effector cells, such as human and murine cholangiocytes and human hepatic stellate cells. Conclusion We present a large international PSC cohort, and report genetic loci associated with PSC disease progression. For liver transplant-free survival, we identified a genome-wide significant signal and demonstrated expression of the candidate gene RSPO3 in key liver-resident effector cells. This warrants further assessments of the role of this potential key PSC modifier gene.

AbstractBackground & AimsSmall duct primary sclerosing cholangitis (PSC) is phenotypically a mild version of large duct PSC, but it is unknown whether these phenotypes share aetiology. We aimed to characterize their relationship by investigating genetic associations in the human leucocyte antigen (HLA) complex, which represent the strongest genetic risk factors in large duct PSC.MethodsFour classical HLA loci (HLA‐A, HLA‐B, HLA‐C and HLA‐DRB1) were genotyped in 87 small duct PSC patients, 485 large duct PSC patients and 1117 controls across three geographical regions.ResultsHLA‐DRB1*13:01 (OR = 2.0, 95% CI 1.2–3.4, P = 0.01) and HLA‐B*08 (OR = 1.6, 95% CI 1.1–2.4, P = 0.02) were significantly associated with small duct PSC compared with healthy controls. Based on the observed frequency of HLA‐B*08 in small duct PSC, the strongest risk factor in large duct PSC, an estimated 32% (95% CI 4–65%) of this population can be hypothesized to represent early stages or mild variants of large duct PSC. This subgroup may be constituted by small duct PSC patients with inflammatory bowel disease (IBD), which greatly resembled large duct PSC in its HLA association. In contrast, small duct PSC without IBD was only associated with HLA‐DRB1*13:01(P = 0.03) and was otherwise distinctly dissimilar from large duct PSC.ConclusionsSmall duct PSC with IBD resembles large duct PSC in its HLA association and may represent early stages or mild variants of large duct disease. Different HLA associations in small duct PSC without IBD could indicate that this subgroup is a different entity. HLA‐DRB1*13:01 may represent a specific risk factor for inflammatory bile duct disease.