Assessment of eating disorder symptoms, compulsive exercise, body dissatisfaction and depression in Swedish national team gymnasts, with a one-year follow-up.

PURPOSE: The purpose of this study was to explore changes in symptoms of eating disorders, compulsive exercise, and depression, between two assessments 12 months apart, among elite gymnasts. METHOD: Factors related to the development of mental health symptoms in male and female Swedish national team gymnasts were investigated using baseline and 1-year follow-up scores in two subscales of the Eating Disorders Inventory 3; drive for thinness and body dissatisfaction, two subscales of the Compulsive Exercise Test; avoidance and rule-driven behavior and exercise for weight control, and the Montgomery-Åsberg Depression Rating Scale-Self report (MADRS-S). Linear mixed models were used to investigate the influence of drive for thinness, exercise for weight control, avoidance and rule-driven behavior, and MADRS-S on body dissatisfaction. RESULTS: Body dissatisfaction increased from baseline to the follow-up assessment, while drive for thinness and depression remained stable. Symptoms of eating disorders and depression were generally low in this group of elite gymnasts at both assessments. Drive for thinness, exercise for weight control, and symptoms of depression were associated with body dissatisfaction. DISCUSSION: Our findings indicate that there were no significant changes over time in eating disorders and depression symptoms but significant associations with body dissatisfaction. Furthermore, we found independent effects of drive for thinness, exercise for weight control and symptoms of depression for body dissatisfaction.

Strengths of associations between depressive symptoms and loneliness, perfectionistic concerns, risky alcohol use and physical activity across levels of sleep quality in Swedish university students: A cross-sectional study.

Previous research shows that sleep quality may interact with some other predictors of depression, such that poor sleep could strengthen the association between these factors and depression. We aimed to determine the presence of statistical interactions between sleep quality and loneliness, risky alcohol use, perfectionistic concerns and/or physical inactivity in relation to depressive symptoms. Further, we aimed to describe the functional form of the statistical interactions and associations. We used a cross-sectional design and included 4262 Swedish university students. All measures were self-reported, sleep quality was measured with the Pittsburgh Sleep Quality Index, and depressive symptoms with the short-form Depression, Anxiety and Stress Scale. Regression models of increasing complexity (linear and non-linear, with and without interactions) were compared to determine the presence of associations and statistical interactions, and to explore the best functional form for these associations and interactions. Out-of-sample R2 from repeated cross-validation was used to select the final models. We found that sleep quality was associated with depressive symptoms in all final models. Sleep quality showed a linear interaction with perfectionistic concerns in relation to depressive symptoms, such that perfectionistic concerns were more strongly associated with depressive symptoms when sleep quality was poor. Loneliness, risky alcohol use and physical inactivity were non-linearly associated with depressive symptoms but did not interact with sleep quality. We concluded that out of the four examined variables, only perfectionistic concerns interacted with sleep quality in relation to depressive symptoms. This interaction was weak and explained little of the overall variance in depressive symptoms.

Perceived knowledge gained from school-based sexuality education - results from a national population-based survey among young people in Sweden.

BACKGROUND: School-based sexuality education is a core component of securing young people's right to attain health equity regarding sexual and reproductive health and rights. This paper aims to explore how perceived knowledge (sufficient or insufficient) of taking care of one's sexual health is associated with knowledge gained from school-based sexuality education and social determinants. METHODS: The data material is drawn from a population-based survey conducted in Sweden in 2015. The survey had 7755 respondents and a response rate of 26%. To explore the aim descriptive statistics and logistic regression models were used. RESULTS: Our results show that perceived insufficient knowledge from school-based sexuality education was associated with higher odds of reporting not being able to take care of one's sexual health. The highest significant excess risk for insufficient knowledge was found among young people from sexual minorities. CONCLUSIONS: Young people in Sweden do not have equal abilities to receive knowledge needed to take care of their sexual health and thus attain sexual health literacy. There is an unequal distribution of perceived knowledge, and LGBTQI+ youth particularly face barriers in using school-based sexuality education as a resource for sexual health literacy.

Lifestyle behaviors in Swedish university students before and during the first six months of the COVID-19 pandemic: a cohort study.

BACKGROUND: Changes in Swedish university students' lifestyle behaviors during the COVID-19 pandemic are unknown. This study aimed to assess physical activity, sitting time, meal frequency and risk substance use (alcohol, tobacco, and illicit use of drugs) in Swedish university students before and during the first six months of the COVID-19 pandemic, for all and stratified by age and sex. METHODS: Data were obtained from the Sustainable University Life cohort study in which web-based surveys were sent to university students repeatedly for one year. Baseline assessment (before the pandemic) was between August 2019-March 2020, follow-up 1 (FU1) between March-June 2020, and follow-up 2 (FU2) between June-September 2020. Participants reported weekly minutes of physical activity, daily sitting hours, meal frequency by weekly intake of different meals, and motivation for eating irregularly, if so. Also, harmful use of alcohol, tobacco and illicit drugs was assessed. Population means and differences with 95% confidence intervals (95% CI) in lifestyle behaviors between time points were calculated with Generalized Estimating Equations. RESULTS: 1877 students (73% women, mean age 26.5 years) answered the baseline survey. Weekly exercise decreased by -5.7 min (95% CI: -10.0, -1.5) and -7.7 min (95% CI: -12.6, -2.8) between baseline and FU1 and FU2, respectively. Weekly daily activities increased by 5.6 min (95% CI: 0.3, 11.7) and 14.2 min (95% CI: 7.9, 20.5) between baseline and FU1 and FU2. Daily sitting time decreased by -1.4 h (95% CI: -1.7, -1.2) between baseline and FU2. Breakfast intake increased by 0.2 days per week (95% CI: 0.1, 0.3) between baseline and FU2. Lunch intake decreased by -0.2 days per week (95% CI: -0.2, -0.1) between baseline and FU1 and by -0.2 days per week (95% CI: -0.3, -0.0) between baseline and FU2. Dinner intake decreased by -0.1 days per week (95% CI: -0.2, -0.0) between baseline and both FU1 and FU2. Only minor differences in risk substance use were observed. Similar changes were observed in analyses stratified by age and sex. CONCLUSIONS: Lifestyle behaviors in Swedish university students slightly improved during the first six months of the COVID-19 pandemic compared to before. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04465435 . 10/07/2020.

Female adolescent elite handball players are more susceptible to shoulder problems than their male counterparts.

PURPOSE: Shoulder problems are frequent among senior elite handball players. The objective of this study was to assess the prevalence of shoulder problems among adolescent elite handball players and to investigate potential differences in gender, school grade, playing position and playing level. METHODS: During the 2014 and 2015 pre-season periods, 471 players (age 15-18 years, 54% female) completed a comprehensive baseline questionnaire regarding history of any shoulder pain and shoulder problems experienced during the past season. The players were monitored weekly for one competition season (September-April) regarding shoulder problems and the amount of match and training. Generalised linear models with a binomial link function were used to calculate a prevalence ratio (PR) with 95% confidence interval (CI) to compare the subgroups of players. RESULTS: In total, 110 players (23%) reported having substantial shoulder problems (defined as moderate/severe reduction in training volume, or moderate/severe reduction in performance, or complete inability to participate) at some point during the follow-up season, of which almost half reported complete inability to participate. Of those players reporting substantial problems, 43% (95% CI 39-48) did so for at least 3 consecutive weeks during the season. The prevalence was significantly higher in female players (PR 1.46, 95% 1.04-2.06) and in backcourt players (PR 1.58, 95% CI 1.08-2.32), but no differences were found for school grade (PR 1.21 95% CI 0.88-1.67) or playing level (PR 1.09 95% CI 0.76-1.56). CONCLUSIONS: The prevalence of substantial shoulder problems in adolescent elite handball players is high, especially among females, and this warrants further studies on risk factors for shoulder injury and the development of prevention strategies in handball players already before the age of 15. These findings also highlight the importance of introducing a clinical monitoring programme on a routine basis and improving the medical support, taking gender-related aspects into consideration, at handball-profiled secondary schools. LEVEL OF EVIDENCE: II.

Dense genotyping of immune-related loci identifies HLA variants associated with increased risk of collagenous colitis.

OBJECTIVE: Collagenous colitis (CC) is a major cause of chronic non-bloody diarrhoea, particularly in the elderly female population. The aetiology of CC is unknown, and still poor is the understanding of its pathogenesis. This possibly involves dysregulated inflammation and immune-mediated reactions in genetically predisposed individuals, but the contribution of genetic factors to CC is underinvestigated. We systematically tested immune-related genes known to impact the risk of several autoimmune diseases for their potential CC-predisposing role. DESIGN: Three independent cohorts of histologically confirmed CC cases (N=314) and controls (N=4299) from Sweden and Germany were included in a 2-step association analysis. Immunochip and targeted single nucleotide polymorphism (SNP) genotype data were produced, respectively, for discovery and replication purposes. Classical human leucocyte antigen (HLA) variants at 2-digit and 4-digit resolution were obtained via imputation from single marker genotypes. SNPs and HLA variants passing quality control filters were tested for association with CC with logistic regression adjusting for age, sex and country of origin. RESULTS: Forty-two markers gave rise to genome-wide significant association signals, all contained within the HLA region on chromosome 6 (best p=4.2×10-10 for SNP rs4143332). Among the HLA variants, most pronounced risk effects were observed for 8.1 haplotype alleles including DQ2.5, which was targeted and confirmed in the replication data set (p=2.3×10-11; OR=2.06; 95% CI (1.67 to 2.55) in the combined analysis). CONCLUSIONS: HLA genotype associates with CC, thus implicating HLA-related immune mechanisms in its pathogenesis.

Fine mapping seronegative and seropositive rheumatoid arthritis to shared and distinct HLA alleles by adjusting for the effects of heterogeneity.

Despite progress in defining human leukocyte antigen (HLA) alleles for anti-citrullinated-protein-autoantibody-positive (ACPA(+)) rheumatoid arthritis (RA), identifying HLA alleles for ACPA-negative (ACPA(-)) RA has been challenging because of clinical heterogeneity within clinical cohorts. We imputed 8,961 classical HLA alleles, amino acids, and SNPs from Immunochip data in a discovery set of 2,406 ACPA(-) RA case and 13,930 control individuals. We developed a statistical approach to identify and adjust for clinical heterogeneity within ACPA(-) RA and observed independent associations for serine and leucine at position 11 in HLA-DRß1 (p = 1.4 × 10(-13), odds ratio [OR] = 1.30) and for aspartate at position 9 in HLA-B (p = 2.7 × 10(-12), OR = 1.39) within the peptide binding grooves. These amino acid positions induced associations at HLA-DRB1(∗)03 (encoding serine at 11) and HLA-B(∗)08 (encoding aspartate at 9). We validated these findings in an independent set of 427 ACPA(-) case subjects, carefully phenotyped with a highly sensitive ACPA assay, and 1,691 control subjects (HLA-DRß1 Ser11+Leu11: p = 5.8 × 10(-4), OR = 1.28; HLA-B Asp9: p = 2.6 × 10(-3), OR = 1.34). Although both amino acid sites drove risk of ACPA(+) and ACPA(-) disease, the effects of individual residues at HLA-DRß1 position 11 were distinct (p < 2.9 × 10(-107)). We also identified an association with ACPA(+) RA at HLA-A position 77 (p = 2.7 × 10(-8), OR = 0.85) in 7,279 ACPA(+) RA case and 15,870 control subjects. These results contribute to mounting evidence that ACPA(+) and ACPA(-) RA are genetically distinct and potentially have separate autoantigens contributing to pathogenesis. We expect that our approach might have broad applications in analyzing clinical conditions with heterogeneity at both major histocompatibility complex (MHC) and non-MHC regions.

A prospective cohort study identifying risk factors for shoulder injuries in adolescent elite handball players: the Karolinska Handball Study (KHAST) study protocol.

BACKGROUND: Handball is a physical contact sport that includes frequent overhead throwing, and this combination leads to a high rate of shoulder injuries. Several factors have been associated with shoulder injuries in overhead athletes, but strong scientific evidence is lacking for most suggested risk factors. We therefore designed the Karolinska Handball Study (KHAST) with the aim to identify risk factors for shoulder injuries in adolescent male and female elite handball players studying at handball-profiled secondary schools in Sweden. Secondary objectives are to investigate whether shoulder function changes during the competition season and whether the physical profile of the players changes during their time in secondary school. METHODS: Players aged 15 to 19 years were included during the pre-season period of the 2014-2015 and the 2015-2016 seasons. At inclusion, players signed informed consent and filled in a questionnaire regarding playing position, playing level, previous handball experience, history of shoulder problems and athletic identity. Players also completed a detailed test battery at baseline evaluating the shoulder, neck and trunk. Players were then prospectively monitored weekly during the 2014-2015 and/or 2015-2016 competitive seasons regarding injuries and training/match workload. Results from the annual routine physical tests in the secondary school curriculum including bench press, deep squat, hand grip strength, clean lifts, squat jumps, counter movement jumps, <30 m sprints, chins, dips and Cooper's test will be collected until the end of the competitive season 2017-2018. The primary outcome is the incidence of shoulder injuries and shoulder problems. The secondary outcome is the prevalence of shoulder injuries and shoulder problems. DISCUSSION: Shoulder problems are frequent among handball players and a reduction of these injuries is therefore warranted. However, in order to introduce appropriate preventive measures, a detailed understanding of the underlying risk factors is needed. Our study has a high potential to identify important risk factors for shoulder injuries in adolescent elite handball players owing to a large study sample, a high response rate, data collection during consecutive seasons, and recording of potential confounding factors.

An Immunochip-based interaction study of contrasting interaction effects with smoking in ACPA-positive versus ACPA-negative rheumatoid arthritis.

OBJECTIVE: To investigate the gene-environment interaction between smoking and single nucleotide polymorphisms (SNPs), using Immunochip material, on the risk of developing either of two serologically defined subsets of RA. METHODS: Interaction between smoking and 133,648 genetic markers from the Immunochip was examined for two RA subsets, defined by the presence or absence of ACPA. A total of 1590 ACPA-positive and 891 ACPA-negative cases were compared with 1856 controls in the Swedish Epidemiological Investigation of RA (EIRA) case-control study. Logistic regression models were used to determine the presence of interaction. The proportion attributable to interaction was calculated for each smoking-SNP pair. Replication was carried out in an independent dataset from northern Sweden. To further validate and extend the results, interaction analysis was also performed using genome-wide association studies data on EIRA individuals. RESULTS: In ACPA-positive RA, 102 SNPs interacted significantly with smoking, after Bonferroni correction. All 102 SNPs were located in the HLA region, mainly within the HLA class II region, 51 of which were replicated. No additional loci outside chromosome 6 were identified in the genome-wide association studies validation. After adjusting for HLA-DRB1 shared epitope, 15 smoking-SNP pairs remained significant for ACPA-positive RA, with 8 of these replicated (loci: BTNL2, HLA-DRA, HLA-DRB5, HLA-DQA1, HLA-DOB and TAP2). For ACPA-negative RA, no smoking-SNP pairs passed the threshold for significance. CONCLUSION: Our study presents extended gene variation patterns involved in gene-smoking interaction in ACPA-positive, but not ACPA-negative, RA. Notably, variants in HLA-DRB1 and those in additional genes within the MHC class II region, but not in any other gene regions, showed interaction with smoking.

Cigarette smoking, antiphospholipid antibodies and vascular events in Systemic Lupus Erythematosus.

OBJECTIVE: Smoking can induce autoantibodies in persons who are genetically predisposed to rheumatoid arthritis. We investigated the association between smoking and antiphospholipid antibodies (aPL) in systemic lupus erythematosus (SLE), a question not previously addressed. Further, we explored the relationship between smoking, aPL and vascular events (arterial and venous, VE). METHODS: In this cross-sectional study, clinical evaluation and questionnaire data were collected from 367 prevalent SLE patients. At the same time, we measured aPL (anticardiolipin (aCL), anti-ß2 glycoprotein-1 (aß2GP1) antibodies IgG/IgM/IgA, and lupus anticoagulant (LA)), and a large set of other SLE-associated autoantibodies for comparison. Association analyses using logistic regression models with smoking, (ever, former and current with never as reference) and antibody status as outcome variable were performed. As a secondary outcome, we investigated the associations between aPL, smoking and VE. RESULTS: In multivariable-adjusted models ever, and in particular former, cigarette smoking was associated with the most pathogenic aPL; LA, aCL IgG and aß2GP1 IgG. Other SLE-associated autoantibodies were not associated with smoking. The combination of smoking and aPL was strongly associated with VE. We noted a positive interaction between smoking-LA and smoking-'triple aPL' positivity for previous VE. CONCLUSIONS: We investigated a large set of commonly occurring autoantibodies in SLE, but only aPL were positively associated with a history of smoking. This association was especially apparent in former smokers. Among ever regular smokers who were aPL positive, we observed a strikingly high frequency of former VE. The underlying mechanisms and temporality between smoking, aPL and VE need further investigations.

Genetic risk scores and number of autoantibodies in patients with rheumatoid arthritis.

OBJECTIVE: Certain HLA-DRB1 alleles and single-nucleotide polymorphisms (SNPs) are associated with rheumatoid arthritis (RA). Our objective was to examine the combined effect of these associated variants, calculated as a cumulative genetic risk score (GRS) on RA predisposition, as well as the number of autoantibodies (none, one or two present). METHOD: We calculated four GRSs in 4956 patients and 4983 controls from four European countries. All four scores contained data on 22 non-HLA-risk SNPs, and three scores also contained HLA-DRB1 genotypes but had different HLA typing resolution. Most patients had data on both rheumatoid factor (RF) and anti-citrullinated proteins antibodies (ACPA). The GRSs were standardised (std.GRS) to account for population heterogeneity. Discrimination between patients and controls was examined by receiveroperating characteristics curves, and the four std.GRSs were compared across subgroups according to autoantibody status. RESULTS: The std.GRS improved its discriminatory ability between patients and controls when HLA-DRB1 data of higher resolution were added to the combined score. Patients had higher mean std.GRS than controls (p=7.9×10(-156)), and this score was significantly higher in patients with autoantibodies (shown for both RF and ACPA). Mean std.GRS was also higher in those with two versus one autoantibody (p=3.7×10(-23)) but was similar in patients without autoantibodies and controls (p=0.12). CONCLUSIONS: The GRS was associated with the number of autoantibodies and to both RF and ACPA positivity. ACPA play a more important role than RF with regards to the genetic risk profile, but stratification of patients according to both RF and ACPA may optimise future genetic studies.

Thyroxin substitution and the risk of developing rheumatoid arthritis; results from the Swedish population-based EIRA study.

OBJECTIVES: Hypothyroidism in iodine-repleted areas is usually of autoimmune nature and leads to chronic thyroxin substitution. It shares some risk factors with anti-citrullinated peptide antibodies (ACPA)-positive rheumatoid arthritis (RA). We asked whether thyroxin substitution associated with risk of ACPA-positive or ACPA-negative RA, and whether interactions with established risk factors were present. METHODS: Data from a population-based case-control study with incident RA cases were analysed (1998 adult cases, 2252 controls). Individuals reporting thyroxin substitution were compared with those without thyroxin, by calculating OR with 95% CI, excluding participants reporting non-autoimmune causes for thyroxin substitution (thyroid cancer, iodine-containing drugs). Interaction was evaluated by attributable proportion (AP) with 95% CI. RESULTS: Thyroxin substitution was associated with a twofold risk of both ACPA-positive (OR=1.9, 95% CI 1.4 to 2.6) and ACPA-negative RA (OR=2.1, 95% CI 1.5 to 3.1). For ACPA-positive RA, the risk associated with the combination thyroxin+ HLA-DRB1 shared epitope alleles (SE) was much higher (OR=11.8, 95% CI 6.9 to 20.0) than for thyroxin (OR=1.4, 95% CI 0.7 to 3.0) or SE (OR=5.7, 95% CI 4.6 to 6.9) alone, indicating a strong interaction (AP=0.5, 95% CI 0.2 to 0.8). Thyroxin substitution interacted non-significantly with smoking (AP=0.4, 95% CI 0.0 to 0.7; OR thyroxin+smoking=3.6, thyroxin only=1.5, smoking only=1.8). Thyroxin did not interact with the PTPN22*R620W allele. CONCLUSIONS: Thyroxin users had a doubled risk of both ACPA-positive and ACPA-negative RA. The risk of ACPA-positive RA was manifold if they smoked or carried the SE. Furthermore, although joint symptoms can be a manifestation of hypothyroidism, physicians might consider whether it could be an early manifestation of RA.

Parity and the risk of developing rheumatoid arthritis: results from the Swedish Epidemiological Investigation of Rheumatoid Arthritis study.

OBJECTIVE: To study the impact of parity history on the risk of antibodies to citrullinated peptide antigens (ACPA) positive and ACPA-negative rheumatoid arthritis (RA), in different age-groups. METHOD: Data from a population-based case-control study of female incident RA cases were analysed (2035 cases and 2911 controls, aged 18-70 years ). Parity history was assessed through a questionnaire. Parous women were compared with nulliparous, by calculating odds ratios (ORs) with 95% confidence interval (CI). RESULTS: Parity was associated with an increased risk of ACPA-negative RA in women aged 18-44 years (OR=2.1, 95% CI 1.4 to 3.2), but not in those aged 45-70 years (OR=0.9, 95% CI 0.7 to 1.3). Among young women, an increased risk of ACPA-negative RA was found in those who gave birth during the year of symptom onset (OR=2.6, 95% CI 1.4 to 4.8) and who were at a young age at first birth (<23) (OR=2.5, 95% CI 1.5 to 4.1). Parity and the postpartum period were not associated with ACPA-positive RA, but older age at first birth was weakly associated with a decreased risk. CONCLUSIONS: The increased risk of ACPA-negative RA in parous women of reproductive age seemed to be associated with an increased postpartum risk and with young age at first birth. Further research is needed to explore the biological mechanisms behind our findings.

Overweight decreases the chance of achieving good response and low disease activity in early rheumatoid arthritis.

AIM: To investigate whether overweight/obesity at diagnosis affects the chances of decrease in disease activity and pain in early rheumatoid arthritis (RA). METHOD: We investigated incident RA cases from the population-based Epidemiological Investigation of risk factors for Rheumatoid Arthritis (EIRA) study (2006-2009, N=495) with clinical follow-up in the Swedish Rheumatology Quality Register. At diagnosis, 93% received disease-modifying antirheumatic drugs (DMARDs) (86% methotrexate). The odds of achieving a good response according to the DAS28-based European League Against Rheumatism (EULAR) criteria, low disease activity (DAS28<3.2), remission (DAS28<2.6) or pain remission (visual analogue scale ≤20 mm) at 3-months and 6-months follow-up, were calculated using logistic regression, adjusting for potential confounders. RESULTS: Significant dose-response relationships were found between Body Mass Index (BMI) and change of disease activity as well as pain at both time points. Patients with BMI ≥25 had 51% lower odds of achieving low disease activity (odds ratio (OR=0.49 (95% CI 0.31 to 0.78)) and 42% lower odds of remission (OR=0.58 (95% CI 0.37 to 0.92)) at the 6-months visit, compared to normal-weight patients. This effect was also present at 3 months, where we also found a 43% decreased odds of pain remission (OR=0.57 (95% CI 0.37 to 0.88)). No effect modification was found for anti-citrullinated protein antibody (CCP)-status, sex, prednisolone treatment or DAS28 at diagnosis. CONCLUSIONS: Overweight at diagnosis significantly decreases the chance of achieving good disease control during the early phase of RA.

Anti-CarP antibodies in two large cohorts of patients with rheumatoid arthritis and their relationship to genetic risk factors, cigarette smoking and other autoantibodies.

INTRODUCTION: In rheumatoid arthritis (RA), several genetic risk factors and smoking are strongly associated with the presence of anticitrullinated protein antibodies (ACPA), while much less is known about risk factors for ACPA-negative RA. Antibodies against carbamylated proteins (anti-CarP) have been described in both ACPA-positive and ACPA-negative RA patients. In this study, we have analysed the relationships among anti-CarP antibodies, ACPA, genetic risk factors (HLA-DRB1 alleles and PTPN22) and smoking in RA. METHODS: Presence of antibodies to carbamylated fetal calf serum (CarP-FCS) and fibrinogen (CarP-Fib) was determined by inhouse ELISAs among RA cases in the Leiden Early Arthritis Clinic (n=846) and in the Swedish Epidemiological Investigation of Rheumatoid Arthritis (n=1985) cohorts. ORs for associations with different HLA-DRB1 alleles, PTPN22 genotypes and smoking were calculated separately for each cohort as well as in meta-analysis in RA subsets defined by the presence/absence of anti-CarP and anticyclic citrullinated peptide (anti-CCP) antibodies. RESULTS: In both cohorts, anti-CarP antibody positivity was mainly detected in the anti-CCP-positive population (49%-73%), but also in the anti-CCP-negative population (8%-14%). No associations between anti-CarP antibodies and HLA-DRB1 shared epitope alleles could be identified, while there were data to support an association between anti-CarP-FCS and HLA-DRB1*03. Further analyses did not reveal any specific associations of anti-CarP antibodies with other HLA-DRB1 alleles, PTPN22 genotypes or smoking. CONCLUSIONS: Anti-CarP antibodies were present in both ACPA-positive and ACPA-negative RA. There were no significant associations among anti-CarP antibodies and HLA-DRB1 alleles, PTPN22 or smoking. These data suggest that different biological mechanisms may underlie anti-CarP versus anti-CCP antibody formation.

Familial risks and heritability of rheumatoid arthritis: role of rheumatoid factor/anti-citrullinated protein antibody status, number and type of affected relatives, sex, and age.

OBJECTIVE: To estimate familial aggregation of rheumatoid arthritis (RA) in 3 large population-representative samples and to test if familial aggregation is affected by rheumatoid factor (RF)/anti-citrullinated protein antibody (ACPA) status, type of relative, sex, and age at onset of RA. METHODS: A register-based nested case-control study was performed in the Swedish total population. Data on patients with RA were ascertained through the nationwide Swedish Patient Register (n = 88,639), the clinical Swedish Rheumatology Quality Register (n = 11,519), and the Epidemiological Investigation of Rheumatoid Arthritis case-control study (n = 2,871). Data on first- and second-degree relatives were obtained through the Swedish Multigeneration Register. Familial risks were calculated using conditional logistic regression. RESULTS: Consistent across data sources, the familial odds ratio for RA was ∼3 in first-degree relatives of RA patients and 2 in second-degree relatives. Familial risks were similar among siblings, parents, and offspring. Familial aggregation was not modified by sex, but was higher in RA patients with early-onset disease and in RF/ACPA-positive RA patients. The observed familial risks were consistent with a heritability of ∼50% for ACPA-positive RA and ∼20% for ACPA-negative RA. CONCLUSION: The pattern of risks suggests that familial factors influence RA in men and women equally and that these factors are of less importance for late-onset RA. Familial factors are more important for seropositive RA, but there is significant familial overlap between seropositive RA and seronegative RA. Even if the familial risk is assumed to be completely due to genetics, the observed risks suggest that heritability of RA is lower than previously reported, in particular for ACPA-negative RA.

Bounds on sufficient-cause interaction.

A common goal of epidemiologic research is to study how two exposures interact in causing a binary outcome. Sufficient-cause interaction is a special type of mechanistic interaction, which requires that two events (e.g. specific exposure levels from two risk factors) are necessary in order for the outcome to occur. Recently, tests have been derived to establish the presence of sufficient-cause interactions, for categorical exposures with at most three levels. In this paper we derive prevalence bounds, i.e. lower and upper bounds on the prevalence of subjects for which sufficient-cause interaction is present. The derived bounds hold for categorical exposures with arbitrary many levels. We apply the bounds to data from a study of gene-gene interaction in the development of Rheumatoid Arthritis. We provide an R-program to estimate the bounds from real data .

Ambient air pollution exposures and risk of rheumatoid arthritis: results from the Swedish EIRA case-control study.

OBJECTIVE: Environmental factors may play a role in the development of rheumatoid arthritis (RA). We examined whether long-term exposures to air pollution were associated with the risk of RA in the Swedish Epidemiological Investigation of Rheumatoid Arthritis Study. METHODS: We studied 1497 incident RA cases and 2536 controls. Local levels of particulate matter (PM10) and gaseous pollutants (sulphur dioxide (SO2) and nitrogen dioxide (NO2)) from traffic and home heating were predicted for all residential addresses. We examined the association of an IQR increase (2 µg/m3 for PM10, 8 µg/m3 for SO2 and 9 µg/m3 for NO2) in each pollutant at different time points before symptom onset and average exposure with the risk of all RA and the risk of the rheumatoid factor and anti-citrullinated protein antibody (ACPA) RA phenotypes. RESULTS: There was no evidence of an increased risk of RA with PM10. Total RA risks were modestly elevated for the gaseous pollutants, but were not statistically significant after adjustment for smoking and education (OR 1.18, 95% CI 0.97 to 1.43 and OR 1.09, 95% CI 0.99 to 1.19 for SO2 and NO2 in the 10th year before onset). Stronger elevated risks were observed for individuals with less than a university education and with the ACPA-negative RA phenotype. CONCLUSIONS: No consistent overall associations between air pollution in the Stockholm area and the risk of RA were observed. However, there was a suggestion of increased risks of RA incidence with increases in NO2 from local traffic and SO2 from home heating sources with stronger associations for the ACPA-negative phenotype.

Genetic and environmental determinants for disease risk in subsets of rheumatoid arthritis defined by the anticitrullinated protein/peptide antibody fine specificity profile.

OBJECTIVES: To increase understanding of the aetiology and pathogenesis of rheumatoid arthritis (RA), genetic and environmental risk factors for RA subsets, defined by the presence or absence of different anticitrullinated protein/peptide antibodies (ACPAs) targeting citrullinated peptides from α-enolase, vimentin, fibrinogen and collagen type II, were investigated. METHODS: 1985 patients with RA and 2252 matched controls from the EIRA case-control cohort were used in the study. Serum samples were assayed by ELISA for the presence of anticyclic citrullinated peptides (anti-CCP) antibodies and four different ACPA fine specificities. Cross-reactivity between ACPAs was examined by peptide absorption experiments. Genotyping was performed for HLA-DRB1 shared epitope (SE) alleles and the PTPN22 gene, while information regarding smoking was obtained by questionnaire. The association of genetic and environmental risk factors with different subsets of RA was calculated by logistic regression analysis. RESULTS: Limited cross-reactivity was observed between different ACPA fine specificities. In total, 17 RA subsets could be identified based on their different ACPA fine specificity profiles. Large differences in association with genetic and environmental determinants were observed between subsets. The strongest association of HLA-DRB1 SE, PTPN22 and smoking was identified for the RA subset which was defined by the presence of antibodies to citrullinated α-enolase and vimentin. CONCLUSION: This study provides the most comprehensive picture to date of how HLA-DRB1 SE, PTPN22 and smoking are associated with the presence of specific ACPA reactivities rather than anti-CCP levels. The new data will form a basis for molecular studies aimed at understanding disease development in serologically distinct subsets of RA.