Complex disease genetics : Utilising targeted sequencing and homogeneous ancestry

The complex disease investigations presented in this thesis aimed to provide new information regarding underlying genetics by using targeted sequencing and ethnically homogeneous cohorts. This work moved past current methodologies and addressed data stratification issues, that might have been hindering new findings. The results contribute to a more comprehensive view of the genetics of ankylosing spondylitis (AS) and breast cancer (BC), in Sweden. Paper-I presents a sex-stratified analysis of a Swedish AS cohort that incorporated both common and rare variants. Single variant and aggregate tests both showed different signals in AS male and female patients, previously masked. Specifically, the RUNX3 locus in males (univariate test: rs7414934, OR=2.58, p=1.7x10-5) and MICB in females (SKAT: 27 variants, p=1.2x10-6; rs3828903, OR=4.62, p=6.2x10-13) exceeded discovery thresholds. In the functional follow up of these loci, risk alleles appear to regulate the expression of genes in multiple tissues. Also, the results highlight the importance of disease regulation from different haplotypes and loci breakdown proved that Sweden’s genetic architecture might be critical for AS studies. Paper-II is a replication study, in our modest-sized Swedish cohort, of AS associations, previously discovered in populations of British origin, Initially, power calculations assessed that the Swedish cohort had the power to replicate only published associated markers with high effect (OR &gt; 7), e.g., HLA-B but the replication analysis revealed three associated loci (ORrange:1.9-2.7). Notably, the multiplicated HLA-B marker (rs4349859) was not in HWE equilibrium. Population structure differences could not explain this replication pattern. However, sequencing resolution revealed fine-scale differences with repositioned association signals in the known loci. Specifically, the identification of two CCHCR1 protective haplotypes (OR: 0.14/0.3) that affect other MHC gene expression through eQTLs, provided the first suggestion of the differential function of known associated loci with cis gene regulation. Paper-III provides the first fingerprint of the somatic mutation profile of Swedish BC. The significantly mutated genes were PIK3CA (28%), TP53 (21%) and CDH1 (16%) while histone-modifying genes (e.g., KMT2C and ARID1A: together 28%) exhibited an increased somatic mutation prevalence, not observed previously. Additionally, within the patients that did not receive neoadjuvant treatment, there were distinct age groups with different mutational profiles and differential APOBEC signature driving genes. Taken together, these studies emphasize the contribution to the underlying genetics deriving from smaller ethnic populations, when assessed with a shift in methodology to account for biological bias, like sex and age. The results will hopefully assist and guide other genetic studies of human complex disease.Exact room will be known the 12th August. Booking system was down due to summer vacation</p

Allele frequency spectrum of known ankylosing spondylitis associated variants in a Swedish population

Objective: The genetic predisposition to ankylosing spondylitis (AS) has been most widely studied in cohorts with European ancestry. However, within Europe, disease prevalence is higher in Sweden. Given this, we aimed to characterize known AS susceptibility variants in a homogeneous Swedish data set, assessing reproducibility and direction of effect. Method: The power to detect association within an existing Swedish targeted sequencing study (381 controls; 310 AS cases) was examined, and a set of published associations (n = 151) was intersected with available genotypes. Association to disease was calculated using logistic regression accounting for population structure, and HLA-B27 status was determined with direct polymerase chain reaction genotyping. Results: The cases were found to be 92.3% HLA-B27 positive, with the data set showing &gt;= 80% predictive power to replicate associations, with odds ratios &gt;= 1.6 over a range of allele frequencies (0.1-0.7). Thirty-four markers, representing 23 gene loci, were available for investigation. The replicated variants tagged MICA and IL23R loci (p &lt; 1.47 x 10(-3)), with variable direction of effect noted for gene loci IL1R1 and MST1. Conclusion: The Swedish data set successfully replicated both major histocompatibility complex (MHC) and non-MHC loci, and revealed a different replication pattern compared to discovery data sets. This was possibly due to population demographics, including HLA-B27 frequency and measured comorbidities

Targeted sequencing reveals the somatic mutation landscape in a Swedish breast cancer cohort

Breast cancer (BC) is a genetically heterogeneous disease with high prevalence in Northern Europe. However, there has been no detailed investigation into the Scandinavian somatic landscape. Here, in a homogeneous Swedish cohort, we describe the somatic events underlying BC, leveraging a targeted next-generation sequencing approach. We designed a 20.5 Mb array targeting coding and regulatory regions of genes with a known role in BC (n = 765). The selected genes were either from human BC studies (n = 294) or from within canine mammary tumor associated regions (n = 471). A set of predominantly estrogen receptor positive tumors (ER +  85%) and their normal tissue counterparts (n = 61) were sequenced to ~ 140 × and 85 × mean target coverage, respectively. MuTect2 and VarScan2 were employed to detect single nucleotide variants (SNVs) and copy number aberrations (CNAs), while MutSigCV (SNVs) and GISTIC (CNAs) algorithms estimated the significance of recurrent somatic events. The significantly mutated genes (q ≤ 0.01) were PIK3CA (28% of patients), TP53 (21%) and CDH1 (11%). However, histone modifying genes contained the largest number of variants (KMT2C and ARID1A, together 28%). Mutations in KMT2C were mutually exclusive with PI3KCA mutations (p ≤ 0. 001) and half of these affect the formation of a functional PHD domain. The tumor suppressor CDK10 was deleted in 80% of the cohort while the oncogene MDM4 was amplified. Mutational signature analyses pointed towards APOBEC deaminase activity (COSMIC signature 2) and DNA mismatch repair (COSMIC signature 6). We noticed two significantly distinct patterns related to patient age; TP53 being more mutated in the younger group (29% vs 9% of patients) and CDH23 mutations were absent from the older group. The increased somatic mutation prevalence in the histone modifying genes KMT2C and ARID1A distinguishes the Swedish cohort from previous studies. KMT2C regulates enhancer activation and assists tumor proliferation in a hormone-rich environment, possibly pointing to a role in ER + BC, especially in older cases. Finally, age of onset appears to affect the mutational landscape suggesting that a larger age-diverse population incorporating more molecular subtypes should be studied to elucidate the underlying mechanisms

Association of Protective HLA-A With HLA-B*27 Positive Ankylosing Spondylitis

Objectives: To further elucidate the role of the MHC in ankylosing spondylitis by typing 17 genes, searching for HLA-B∗27 independent associations and assessing the impact of sex on this male biased disease. Methods: High-confidence two-field resolution genotyping was performed on 310 cases and 2196 controls using an n-1 concordance method. Protein-coding variants were called from next-generation sequencing reads using up to four software programs and the consensus result recorded. Logistic regression tests were applied to the dataset as a whole, and also in stratified sets based on sex or HLA-B∗27 status. The amino acids driving association were also examined. Results: Twenty-five HLA protein-coding variants were significantly associated to disease in the population. Three novel protective associations were found in a HLA-B∗27 positive population, HLA-A∗24:02 (OR = 0.4, CI = 0.2–0.7), and HLA-A amino acids Leu95 and Gln156. We identified a key set of seven loci that were common to both sexes, and robust to change in sample size. Stratifying by sex uncovered three novel risk variants restricted to the female population (HLA-DQA1∗04.01, -DQB1∗04:02, -DRB1∗08:01; OR = 2.4–3.1). We also uncovered a set of neutral variants in the female population, which in turn conferred strong effects in the male set, highlighting how population composition can lead to the masking of true associations. Conclusion: Population stratification allowed for a nuanced investigation into the tightly linked MHC region, revealing novel HLA-B∗27 signals as well as replicating previous HLA-B∗27 dependent results. This dissection of signals may help to elucidate sex biased disease predisposition and clinical progression.Funding agencies: Swedish Research Council, FORMAS (Dnr 2012-1531), Knut and Alice Wallenberg Foundation (Dnr 2012-0268), Swedish Research Council for Medicine and Health (D0283001 and Dnr 2018-02399), the Swedish Rheumatism Association, and King Gustaf V’s 80-year Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.</p

Common genetic variation in the autoimmune regulator (AIRE) locus is associated with autoimmune Addisons disease in Sweden

Autoimmune Addisons disease (AAD) is the predominating cause of primary adrenal failure. Despite its high heritability, the rarity of disease has long made candidate-gene studies the only feasible methodology for genetic studies. Here we conducted a comprehensive reinvestigation of suggested AAD risk loci and more than 1800 candidate genes with associated regulatory elements in 479 patients with AAD and 2394 controls. Our analysis enabled us to replicate many risk variants, but several other previously suggested risk variants failed confirmation. By exploring the full set of 1800 candidate genes, we further identified common variation in the autoimmune regulator (AIRE) as a novel risk locus associated to sporadic AAD in our study. Our findings not only confirm that multiple loci are associated with disease risk, but also show to what extent the multiple risk loci jointly associate to AAD. In total, risk loci discovered to date only explain about 7% of variance in liability to AAD in our study population.Funding Agencies|Swedish Research Council; Torsten and Ragnar Soderberg Foundations; European Union Seventh Framework Programme [201167]; Stockholm County Council; Karolinska Institutet; Swedish Society for Medical Research; Swedish Society of Medicine; NovoNordisk Foundation; Tore Nilsons Foundation for Medical Research; Swedish Research Council Formas; Knut and Alice Wallenberg Foundation; Marianne and Marcus Wallenberg Foundation; Swedish Reumatism Foundation; King Gustaf Vs 80-year Foundation; Ake Wiberg Foundation</p

Extended exome sequencing identifies BACH2 as a novel major risk locus for Addison's disease

BackgroundAutoimmune disease is one of the leading causes of morbidity and mortality worldwide. In Addison's disease, the adrenal glands are targeted by destructive autoimmunity. Despite being the most common cause of primary adrenal failure, little is known about its aetiology. MethodsTo understand the genetic background of Addison's disease, we utilized the extensively characterized patients of the Swedish Addison Registry. We developed an extended exome capture array comprising a selected set of 1853 genes and their potential regulatory elements, for the purpose of sequencing 479 patients with Addison's disease and 1394 controls. ResultsWe identified BACH2 (rs62408233-A, OR = 2.01 (1.71-2.37), P = 1.66 x 10(-15), MAF 0.46/0.29 in cases/controls) as a novel gene associated with Addison's disease development. We also confirmed the previously known associations with the HLA complex. ConclusionWhilst BACH2 has been previously reported to associate with organ-specific autoimmune diseases co-inherited with Addison's disease, we have identified BACH2 as a major risk locus in Addison's disease, independent of concomitant autoimmune diseases. Our results may enable future research towards preventive disease treatment