Bidirectional association between inflammatory bowel disease and type 1 diabetes: a nationwide matched cohort and case-control study.

Background: Co-occurrence of inflammatory bowel disease (IBD) and type 1 diabetes (T1D) has been linked to poor clinical outcomes, but evidence on their bidirectional associations remain scarce. This study aims to investigate their bidirectional associations. Methods: A nationwide matched cohort and case-control study with IBD patients identified between 1987 and 2017. The cohort study included 20,314 IBD patients (≤28 years; Crohn's disease [CD, n = 7277], ulcerative colitis [UC, n = 10,112], and IBD-unclassified [IBD-U, n = 2925]) and 99,200 individually matched reference individuals, with a follow-up until December 2021. The case-control study enrolled 87,001 IBD patients (no age restriction) and 431,054 matched controls. We estimated adjusted hazard ratio (aHR) of incident T1D in the cohort study with flexible parametric survival model and adjusted odds ratio (aOR) of having a prior T1D in the case-control study with conditional logistic regression model, with 95% confidence intervals (CI). Findings: During a median follow-up of 14 years, 116 IBD patients and 353 reference individuals developed T1D. Patients with IBD had a higher hazard of developing T1D (aHR = 1.58 [95% CI = 1.27-1.95]). The hazard was increased in UC (aHR = 2.02 [1.51-2.70]) but not in CD or IBD-U. In the case-control study, a total of 1018 (1.2%) IBD patients and 3496 (0.8%) controls had been previously diagnosed with T1D. IBD patients had higher odds of having prior T1D (aOR = 1.36 [1.26-1.46]). Such positive association was observed in all IBD subtypes. The sibling comparison analyses showed similar associations between IBD and T1D (aHR = 1.44 [0.97-2.15] and aOR = 1.32 [1.18-1.49]). Interpretation: Patients with IBD had a moderately increased hazard of developing T1D and higher odds of having prior T1D. Their bidirectional associations may be partially independent of shared familial factors. Funding: European Crohn's and Colitis Organisation, Stiftelsen Professor Nanna Svartz Fond, SSMF (project#: PG-23-0315-H-02), Ruth and Richard Julin Foundation; and FORTE (project#: 2016-00424).

Birth Weight, Gestational Age, and Risk of Pediatric-Onset MASLD.

Importance: Metabolic dysfunction-associated steatotic liver disease (MASLD) has become the most common chronic liver disease worldwide and is increasingly being diagnosed at younger ages, affecting more than one-third of young people with obesity. Objective: To evaluate associations between perinatal conditions and risk of MASLD and associated progressive liver disease. Design, Setting, and Participants: This nationwide, population-based case-control study included all biopsy-confirmed cases of MASLD in Sweden. Individuals aged 25 years or younger (hereafter, young individuals) with biopsy-proven MASLD between January 1, 1992, and December 31, 2016, were matched to up to 5 general population control individuals. Granular data on maternal and perinatal characteristics were retrieved from the Swedish Medical Birth Register. Data were analyzed from June 2023 to June 2024. Exposures: Birth weight (low [<2500 g], reference [2500 to <4000 g], or high [≥4000 g]), gestational age (GA), and birth weight for GA (small for GA [SGA; <10th percentile], appropriate for GA [10th-90th percentile], or large for GA [LGA; >90th percentile]), compared between patients and matched controls. Main Outcomes and Measures: The main outcome was odds of biopsy-proven MASLD and MASLD-associated progressive liver disease (ie, liver fibrosis or cirrhosis) according to birth weight, GA, and birth weight for GA, adjusted for matching factors. Results: In total, 165 young individuals with biopsy-proven MASLD (median age at diagnosis: 12.0 years [IQR, 4.4-16.9 years]; 100 [60.6%] male) were matched with 717 controls. There was an association between low birth weight and future development of MASLD (adjusted odds ratio [AOR], 4.05; 95% CI, 1.85-8.88) but no association between high birth weight and odds of MASLD (AOR, 0.64; 95% CI, 0.38-1.08) compared with the reference birth weight. An association was seen for SGA (AOR, 3.36; 95% CI, 2.00-5.64) compared with appropriate size for GA (reference category) but not for LGA (AOR, 0.57; 95% CI, 0.27-1.20). Progressive liver disease was more common in individuals born with low birth weight (AOR, 6.03; 95% CI, 1.66-21.87) or SGA (AOR, 4.90; 95% CI, 2.15-11.14). Conclusions and Relevance: In this nationwide study of young individuals with biopsy-proven MASLD, low birth weight and SGA were associated with development of MASLD and progressive liver disease, suggesting a need for structured screening measures to diagnose these conditions early in high-risk individuals.

Diverticular disease and risk of incident major adverse cardiovascular events: A nationwide matched cohort study.

BACKGROUND: An increased risk of cardiovascular disease (CVD) has been reported in patients with diverticular disease (DD). However, there are knowledge gaps about specific risks of each major adverse cardiovascular event (MACE) component. METHODS: This nationwide cohort study included Swedish adults with DD (1987-2017, N=52,468) without previous CVD. DD was defined through ICD codes in the National Patient Register and colorectal histopathology reports from the ESPRESSO study. DD cases were matched by age, sex, calendar year and county of residence to ≤5 population reference individuals (N=194,525). Multivariable-adjusted hazard ratios (aHRs) for MACE up until December 2021 were calculated using stratified Cox proportional hazard models. RESULTS: Median age at DD diagnosis was 62 years and 61% were females. During a median follow-up of 8.6 years, 16,147 incident MACE occurred in individuals with DD, and 48,134 in reference individuals (incidence rates (IRs)=61.4 vs. 43.8/1,000 person-years) corresponding to an aHR of 1.24 (95%CI=1.22-1.27), equivalent to one extra case of MACE for every 6 DD patients followed for 10 years. The risk was increased for ischemic heart disease (IR=27.9 vs. 18.6; aHR=1.36, 95%CI=1.32-1.40), congestive heart failure (IR=23.2 vs. 15.8; aHR=1.26, 95%CI=1.22-1.31), and stroke (IR=18.0 vs. 13.7; aHR=1.15, 95%CI=1.11-1.19). DD was not associated with cardiovascular mortality (IR=18.9 vs. 15.3; aHR=1.01, 95%CI=0.98-1.05). Results remained robust in sibling-controlled analyses. CONCLUSIONS: Patients with DD had a 24% increased risk of MACE compared with reference individuals, but no increased cardiovascular mortality. Future research should confirm these data and examine underlying mechanisms and shared risk factors between DD and CVD.

Convenience Sampling Yields No Evidence of SARS-CoV-2 Infection in Free-Ranging Mammalian Wildlife in Arizona, USA, 2021-23.

Susceptibility of free-ranging US wildlife to SARS-CoV-2 infection has been documented. Nasal or oral swabs and blood from 337 wild mammals (31 species) in Arizona USA, tested for antibodies and by reverse-transcription PCR, did not reveal evidence of SARS-CoV-2. Broader surveillance efforts are necessary to understand the role of wildlife.

Inflammatory eye disease is a risk factor for future microscopic colitis: A nationwide population-based matched case control study.

BACKGROUND: Microscopic colitis (MC) is an inflammatory disorder of the colon. To date, the relationship between inflammatory eye diseases and MC is unclear. OBJECTIVE: To assess whether inflammatory eye disease (iridocyclitis and episcleritis) is a risk factor for MC. METHODS: We conducted a nationwide matched case control study in Sweden leveraging the ESPRESSO-study (a Swedish database containing data on all biopsies from the gastrointestinal tract from 1965 to 2017). In total, we identified 14,338 patients with biopsy-verified MC (diagnosed from 1981 to 2017). Patients with MC were matched (by age, sex, county and year of birth) with 68,753 controls from the general population and the occurrence of preceding inflammatory eye diseases (defined as diagnosis of episcleritis or iridocyclitis) in the two groups was compared. Multivariable adjusted odds ratios (aORs) were calculated using conditional logistic regression conditioned on the matching variables. RESULTS: A majority of patients with MC were women (71.9%) and the median age at MC diagnosis was 63.3 years (interquartile range (IQR) = 50.7-72.6). Some 225 (1.6%) MC patients had an earlier record of inflammatory eye disease compared with 614 (0.9%) in controls. These figures corresponded to an aOR of 1.77 (95% CI = 1.52-2.07) for inflammatory eye diseases in patients with MC. Compared to siblings, the aOR for previous inflammatory eye diseases in MC was 1.52 (95% CI = 1.17-1.98) and patients treated with budesonide, as a proxy for clinically significant disease, had a somewhat higher aOR for previous inflammatory eye diseases. CONCLUSION: Inflammatory eye diseases are more common in patients subsequently being diagnosed with MC. Our findings highlight that these conditions may have shared causes and inflammatory pathways and are of clinical interest to gastroenterologists, ophthalmologists and general practitioners.

Psychiatric Disorders Among 5,800 Patients With Microscopic Colitis: A Nationwide Population-Based Matched Cohort Study.

INTRODUCTION: Microscopic colitis (MC) is an inflammatory condition of the large intestine. Primarily diagnosed in middle-aged and older adults, the incidence of the disease has increased markedly during the past few decades. While MC is associated with a reduced quality of life, large-scale studies on the association with future psychiatric disorders are lacking. METHODS: We conducted a nationwide matched cohort study in Sweden from 2006 to 2021. Through a nationwide histopathology database (the Epidemiology Strengthened by histoPathology Reports in Sweden study), we identified 5,816 patients with a colorectal biopsy consistent with MC. These patients were matched with 21,509 reference individuals from the general population all of whom with no previous record of psychiatric disorders. RESULTS: From 2006 to 2021, 519 patients with MC (median age 64.4 years [interquartile range = 49.5-73.3]) and 1,313 reference individuals were diagnosed with psychiatric disorders (9.9 vs 6.5 events per 1,000 person-years), corresponding to 1 extra case of psychiatric disorder in 29 patients with MC over 10 years. After adjustments, the hazard ratio for psychiatric disorders was 1.57 (95% confidence interval = 1.42-1.74). We found significantly elevated estimates up to 10 years after MC diagnosis and a trend toward higher risk with increasing age. Specifically, we observed increased risks for unipolar depression, anxiety disorders, stress-related disorders, substance abuse, and suicide attempts. In sibling-controlled analysis, the adjusted hazard ratio was 1.76 (95% confidence interval = 1.44-2.15). DISCUSSION: Patients with MC are at increased risk of incident psychiatric disorders compared with the general population.

Reemergence of a Big Brown Bat Lyssavirus rabies Variant in Striped Skunks in Flagstaff, Arizona, USA, 2021-2023.

Background: Throughout the Americas, Lyssavirus rabies (RV) perpetuates as multiple variants among bat and mesocarnivore species. Interspecific RV spillover occurs on occasion, but clusters and viral host shifts are rare. The spillover and host shift of a big brown bat (Eptesicus fuscus) RV variant Ef-W1 into mesocarnivores was reported previously on several occasions during 2001-2009 in Flagstaff, Arizona, USA, and controlled through rabies vaccination of target wildlife. During autumn 2021, a new cluster of Ef-W1 RV cases infecting striped skunks (Mephitis mephitis) was detected from United States Department of Agriculture enhanced rabies surveillance in Flagstaff. The number of Ef-W1 RV spillover cases within a short timeframe suggested the potential for transmission between skunks and an emerging host shift. Materials and Methods: Whole and partial RV genomic sequencing was performed to evaluate the phylogenetic relationships of the 2021-2023 Ef-W1 cases infecting striped skunks with earlier outbreaks. Additionally, real-time reverse-transcriptase PCR (rtRT-PCR) was used to opportunistically compare viral RNA loads in brain and salivary gland tissues of naturally infected skunks. Results: Genomic RV sequencing revealed that the origin of the 2021-2023 epizootic of Ef-W1 RV was distinct from the multiple outbreaks detected from 2001-2009. Naturally infected skunks with the Ef-W1 RV showed greater viral RNA loads in the brain, but equivalent viral RNA loads in the mandibular salivary glands, compared to an opportunistic sample of skunks naturally infected with a South-Central skunk RV from northern Colorado, USA. Conclusion: Considering a high risk for onward transmission and spread of the Ef-W1 RV in Flagstaff, public outreach, enhanced rabies surveillance, and control efforts, focused on education, sample characterization, and vaccination, have been ongoing since 2021 to mitigate and prevent the spread and establishment of Ef-W1 RV in mesocarnivores.

Risk of heart failure in inflammatory bowel disease: a Swedish population-based study.

BACKGROUND AND AIMS: Dysregulation of inflammatory and immune responses has been implicated in the pathogenesis of heart failure (HF). But even if inflammation is a prerequisite for inflammatory bowel disease (IBD), little is known about HF risk in IBD. METHODS: In this Swedish nationwide cohort, patients with biopsy-confirmed IBD were identified between 1969 and 2017 [n = 81 749, Crohn's disease (CD, n = 24 303), ulcerative colitis (UC, n = 45 709), and IBD-unclassified (IBD-U, n = 11 737)]. Each patient was matched with up to five general population reference individuals (n = 382 190) and IBD-free full siblings (n = 95 239) and followed until 31 December 2019. Flexible parametric survival models estimated the adjusted hazard ratio (aHR) and standardized cumulative incidence for HF, with 95% confidence intervals (CI). RESULTS: There were 5582 incident HF identified in IBD patients (incidence rate [IR]: 50.3/10 000 person-years) and 20 343 in reference individuals (IR: 37.9) during a median follow-up of 12.4 years. IBD patients had a higher risk of HF than reference individuals (aHR 1.19, 95% CI 1.15-1.23). This increased risk remained significant ≥20 years after IBD diagnosis, leading to one extra HF case per 130 IBD patients until then. The increased risk was also observed across IBD subtypes: CD (IR: 46.9 vs. 34.4; aHR 1.28 [1.20-1.36]), UC (IR: 50.1 vs. 39.7; aHR 1.14 [1.09-1.19]), and IBD-U (IR: 60.9 vs. 39.0; aHR 1.28 [1.16-1.42]). Sibling-controlled analyses showed slightly attenuated association (IBD: aHR 1.10 [1.03-1.19]). CONCLUSIONS: Patients with IBD had a moderately higher risk of developing HF for ≥20 years after IBD diagnosis than the general population.

Microscopic Colitis and Risk of Incident Psoriasis: A Nationwide Population-Based Matched Cohort Study.

Background: Microscopic colitis (MC) has been associated with several immune-mediated diseases including psoriasis, but earlier research has been limited to psoriasis occurring before MC. Data from large-scale cohort studies investigating MC and risk of future psoriasis are lacking. Objective: To examine the association between MC and psoriasis. Methods: In a nationwide, population-based, matched cohort study in Sweden from 2007 to 2021, we identified 8404 patients with biopsy-verified MC (diagnosed in 2007-2017), 37,033 matched reference individuals, and 8381 siblings without MC. Information on MC was obtained through the ESPRESSO cohort (a Swedish histopathology database with nationwide coverage). Using Cox regression, we calculated hazard ratios (HRs) and 95% confidence intervals (CIs) for psoriasis up until 2021. Results: During a median follow-up of 9.2 years (interquartile range = 6.7-11.7), 179 MC patients and 440 reference individuals were diagnosed with psoriasis (241.1 vs 131.8 events per 100,000 person-years), corresponding to one extra case of psoriasis in 91 patients with MC over 10 years. After adjustment for the matching variables (birth year, sex, county of residence, and calendar period) and level of education, we computed an adjusted hazard ratio (aHR) of 1.82 (95% CI = 1.53-2.17). Stratified by sex, estimates were similar and when examining the aHR across different lengths of follow-up, we found significantly elevated estimates up to 10 years after MC diagnosis. Compared to MC-free siblings, the aHR was 1.85 (95% CI = 1.36-2.51). Conclusion: Patients with MC are at an almost doubled risk of psoriasis compared to the general population. Clinicians need to consider psoriasis in MC patients with skin lesions.

Novel characterization of CASK variant c.1963 A>G (p.Asn655Asp) through whole-exome sequencing in a monochorionic diamniotic twin fetus with significant brain anomalies: A case report.

Whole-exome sequencing is an evolving technology in perinatal diagnosis which allows identification of genetic etiologies that would otherwise go undetermined. In this case report, a 38-year-old Hispanic woman, G5P3013, with a monochorionic diamniotic twin gestation with one fetus displaying significant cranial abnormalities on prenatal ultrasound and magnetic resonance imaging (MRI) of the brain is presented. Fetal anomalies included bilateral ventriculomegaly, absent cavum septum pellucidum, and absent corpus callosum. Diagnostic amniocentesis with chromosome analysis, chromosomal microarray, alpha-fetoprotein, cytomegalovirus, toxoplasmosis, and parvovirus had normal results. Whole-exome sequencing for the anomalous fetus detected a de novo mosaic variant of uncertain significance (VUS) in the calcium/calmodulin dependent serine protein kinase (CASK) gene: c.1963 A > G (p.Asn655Asp). This variant was absent in the normal twin fetus, the mother, and the father. Pathogenic CASK gene mutations are associated with three syndromes: FG syndrome 4, intellectual developmental disorder and microcephaly with pontine and cerebellar hypoplasia (MICPCH), and intellectual developmental disorder with or without nystagmus. Whole-exome sequencing identified a potential etiology for the anomalies detected. The variant likely arose de novo and was the potential cause of the identified cranial abnormalities in one fetus of this monochorionic diamniotic twin gestation. Whole-exome sequencing may provide additional diagnostic utility when standard diagnostic testing is noncontributory.

Long-term risk of myocarditis in patients with inflammatory bowel disease: a nationwide cohort study in Sweden.

OBJECTIVES: Despite a suggested link between inflammatory bowel disease (IBD) and myocarditis, the association has not been well-established. This study aimed to investigate the long-term risk of myocarditis in patients with IBD. METHODS: This nationwide cohort involved all patients with biopsy-confirmed IBD in Sweden (1969-2017) (n=83,264, Crohn's disease [CD, n=24,738], ulcerative colitis [UC, n=46,409], and IBD-unclassified [IBD-U, n=12,117]), general population reference individuals (n=391,344), and IBD-free full siblings (n=96,149), and followed until 2019. Primary outcome was incident myocarditis and secondary outcome was severe myocarditis (complicated with heart failure, death, or readmission). Flexible parametric survival models were used to estimate adjusted hazard ratios (aHR) and cumulative incidence of outcomes, along with 95% confidence intervals (CIs). RESULTS: During a median follow-up of 12 years, there were 256 myocarditis cases in IBD patients (incidence rate [IR]=22.6/100,000 person-years) and 710 in reference individuals (IR=12.9), with an aHR of 1.55 (95%CI: 1.33 to 1.81). The increased risk persisted through 20 years after IBD diagnosis, corresponding to one extra myocarditis case in 735 IBD patients until then. This increased risk was observed in CD (aHR=1.48 [1.11 to 1.97]) and UC (aHR=1.58 [1.30 to 1.93]). IBD was also associated with severe myocarditis (IR: 10.1 vs. 3.5; aHR=2.44 [1.89 to 3.15]), irrespective of IBD subtypes (CD: aHR=2.39 [1.43 to 4.01], UC: aHR=2.82 [1.99 to 4.00], and IBD-U: aHR=3.14 [1.55 to 6.33]). Sibling comparison analyses yielded similar results. CONCLUSIONS: Patients with IBD had an increased risk of myocarditis, especially severe myocarditis, for ≥20 years after diagnosis, but absolute risks were low.

Lyssa excreta: Defining parameters for fecal samples as a rabies virus surveillance method.

It is not possible to systematically screen the environment for rabies virus (RABV) using current approaches. We sought to determine under what conditions RABV is detectable from feces and other accessible samples from infected wildlife to broaden the number of biological samples that could be used to test for RABV. We employed a recently-developed quantitative RT-PCR assay called the "LN34 panlyssavirus real-time RT-PCR assay", which is highly sensitive and specific for all variants of RABV. We harvested and tested brain tissue, fecal, and/or mouth swab samples from 25 confirmed RABV positive bats of six species. To determine if rabies RNA lasts in feces sufficiently long post-defecation to use it as a surveillance tool, we tested fecal samples from 10 bats at the time of sample collection and after 24 hours of exposure to ambient conditions, with an additional test on six bats out to 72 hours. To assess whether we could pool fecal pellets and still detect a positive, we generated dilutions of known positives at 1:1, 1:10, 1:50, and 1:200. For six individuals for which matched brain, mouth swab, and fecal samples were tested, results were positive for 100%, 67%, and 67%, respectively. For the first time test to 24 hours, 63% of feces that were positive at time 0 were still positive after 24 hours, and 50% of samples at 72 hours were positive across all three replicates. Pooling tests revealed that fecal positives were detected at 1:10 dilution, but not at 1:50 or 1:200. Our preliminary results suggest that fecal samples hold promise for a rapid and non-invasive environmental screening system.

Statin use and risk of colorectal cancer in patients with inflammatory bowel disease.

Background: Statin use has been linked to a reduced risk of advanced colorectal adenomas, but its association with colorectal cancer (CRC) in patients with inflammatory bowel disease (IBD) - a high risk population for CRC - remains inconclusive. Methods: From a nationwide IBD cohort in Sweden, we identified 5273 statin users and 5273 non-statin users (1:1 propensity score matching) from July 2006 to December 2018. Statin use was defined as the first filled prescription for ≥30 cumulative defined daily doses and followed until December 2019. Primary outcome was incident CRC. Secondary outcomes were CRC-related mortality and all-cause mortality. Cox regression estimated adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs). Findings: During a median follow-up of 5.6 years, 70 statin users (incidence rate (IR): 21.2 per 10,000 person-years) versus 90 non-statin users (IR: 29.2) were diagnosed with incident CRC (rate difference (RD), -8.0 (95% CIs: -15.8 to -0.2 per 10,000 person-years); aHR = 0.76 (95% CIs: 0.61 to 0.96)). The benefit for incident CRC was duration-dependent in a nested case-control design: as compared to short-term use (30 days to <1 year), the adjusted odd ratios were 0.59 (0.25 to 1.43) for 1 to <2 years of use, 0.46 (0.21 to 0.98) for 2 to <5 years of use, and 0.38 (0.16 to 0.86) for ≥5 years of use (Pfor tread = 0.016). Compared with non-statin users, statin users also had a decreased risk for CRC-related mortality (IR: 6.0 vs. 11.9; RD, -5.9 (-10.5 to -1.2); aHR, 0.56 (0.37 to 0.83)) and all-cause mortality (IR: 156.4 vs. 231.4; RD, -75.0 (-96.6 to -53.4); aHR, 0.63 (0.57 to 0.69)). Interpretation: Statin use was associated with a lower risk of incident CRC, CRC-related mortality, and all-cause mortality. The benefit for incident CRC was duration-dependent, with a significantly lower risk after ≥2 years of statin use. Funding: This research was supported by Forte (i.e., the Swedish Research Council for Health, Working Life and Welfare).

Microscopic colitis and risk of incident rheumatoid arthritis: A nationwide population-based matched cohort study.

BACKGROUND: Microscopic colitis (MC) has been linked to several autoimmune conditions. Results from previous studies on the association with rheumatoid arthritis (RA) have been inconsistent. AIM: To assess the risk of future RA in MC. METHODS: We conducted a nationwide matched cohort study in Sweden of 8179 patients with biopsy-verified MC (diagnosed in 2007-2017), 36,400 matched reference individuals and 8202 siblings without MC, with follow-up until 2021. Information on MC was obtained from all of Sweden's regional pathology registers (n = 28) through the ESPRESSO cohort. Data on incident RA were collected from the National Patient Register. Using Cox regression, we calculated adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs). RESULTS: During a median follow-up of 9.1 years (interquartile range = 6.7-11.7), 73 MC patients and 183 reference individuals from the general population were diagnosed with RA (99 vs. 55 events per 100,000 person-years), equivalent to one extra case of RA in 226 patients with MC followed for 10 years. These rates corresponded to an aHR of 1.83 (95% CI = 1.39-2.41). The aHR was highest during the first year of follow-up (2.31 [95% CI = 1.08-4.97]) and remained significantly elevated up to 5 years after MC diagnosis (aHR 2.16; 95% CI = 1.42-3.30). Compared to siblings, without MC, the aHR was 2.04 (95% CI = 1.18-3.56). CONCLUSION: Patients with MC are at a nearly two-fold risk of developing RA compared to the general population. Knowledge of this increased risk may expedite evaluation for RA in patients with MC presenting with joint symptoms and/or arthralgia, thus preventing delay until RA diagnosis.

Familial coaggregation of MASLD with hepatocellular carcinoma and adverse liver outcomes: Nationwide multigenerational cohort study.

BACKGROUND & AIMS: Metabolic dysfunction-associated steatotic liver disease (MASLD; formerly NAFLD) is the fastest growing cause of hepatocellular carcinoma (HCC) worldwide. However, whether family members of individuals with MASLD also share an increased risk of developing HCC is unknown. METHODS: This nationwide multigenerational cohort study involved family members of all Swedish adults diagnosed with biopsy-proven MASLD (1969-2017), and matched general population comparators. Using the Swedish Multi-generation Register, we identified 38,018 first-degree relatives (FDRs: parents, siblings, offspring) and 9,381 spouses of patients with MASLD, as well as 197,303 comparator FDRs and 47,572 comparator spouses. We used Cox proportional hazards models to calculate adjusted hazard ratios (aHRs) for HCC, major adverse liver outcomes (cirrhosis, decompensated liver disease or liver transplantation), liver-related mortality, extrahepatic cancer, and non-liver-related mortality. RESULTS: Over a median of 17.6 years, the rate of the primary outcome HCC was higher in MASLD FDRs vs. comparator FDRs (13 vs. 8/100,000 person-years [PY]; aHR 1.80, 95% CI 1.36-2.37). The HCC risk was further increased in FDRs of individuals with liver fibrosis/cirrhosis (aHR 2.14, 95% CI 1.07-4.27; PHeterogeneity = 0.03). MASLD FDRs also had higher rates of major adverse liver outcomes (73 vs. 51/100,000 PY; aHR 1.52, 95% CI 1.36-1.69) and liver-related mortality (20 vs. 11/100,000 PY; aHR 2.14, 95% CI 1.67-2.74). MASLD FDRs with any concomitant chronic liver condition experienced accelerated progression of liver disease (aHR 1.47, 95% CI 1.29-1.67). MASLD spouses were at higher risks of major adverse liver outcomes (86 vs. 74/100,000 PY; aHR 1.23, 95% CI 1.01-1.51) and liver-related mortality (25 vs. 19/100,000 PY; aHR 1.93, 95% CI 1.15-3.23), but not of HCC (aHR 1.43, 95% CI 0.87-2.35). CONCLUSIONS: There is distinct familial clustering of adverse liver-related outcomes in families of individuals with biopsy-proven MASLD, with higher relative risks of HCC, progressive liver disease, and liver-related mortality, but absolute risks are low. IMPACT AND IMPLICATIONS: Metabolic dysfunction-associated steatotic liver disease (MASLD; formerly termed NAFLD) clusters in families with high genetic susceptibility and shared environmental risk factors, but the risks of developing hepatocellular carcinoma and other major liver-related outcomes in family members of individuals with MASLD are largely unknown. This large nationwide multigenerational cohort study involving family members (first-degree relatives and spouses) of individuals with biopsy-proven MASLD and of matched general population comparators found slightly increased risks of hepatocellular carcinoma in first-degree relatives, and of developing cirrhosis and liver-related mortality in all family members of individuals with biopsy-proven MASLD. The findings of this study provide large-scale evidence to inform clinical practice guidelines for recommendations on the early identification of individuals at higher risk of liver-related morbidity and mortality.