Corresponding author

1. Associations between maternal socioeconomic position and psoriasis: A cohort study among the offspring of the Danish National Birth Cohort J. Groot1, A.M. Nybo Andersen2, A. Adam2, T.E. Tind Nielsen1,2, C. Blegvad1, and L. Skov1 1Department of Dermatology and Allergy, Herlev and Gentofte Hospital, University of Copenhagen, Hellerup, Denmark 2Section for Epidemiology, Department of Public Health, University of Copenhagen, Copenhagen, Denmark Articledoi: 10.1111/bjd.17091

2. Corresponding author Jonathan Groot, MScPH1,2 1Department of Dermatology and Allergy Gentofte Hospital University of Copenhagen 2Department of Public Health Section of Epidemiology University of Copenhagen

3. Whatis already known? Previous studies have shown that psoriatic comorbidities are inversely associated with socioeconomic position (SEP) The nature of potential associations between SEP and paediatric-onset psoriasishave not been explored

4. Objective This study’s primary aim was to examine whether a social gradient exists in the prevalence of paediatric-onset psoriasis

5. Methods Population and Data collection Data on offspring psoriasis status from an 11-year follow-up of the offspring of the Danish National Birth Cohort (DNBC) was linked to registry data from Statistics Denmark on maternal SEP SEP registry data included: Maternal age at birth Maternal educational attainment (according to ISCED levels*) Maternal labour market attachment (SOCIO13 codes**) Equivalised household income *International Standard Classification of Education **Codes from the Employment Classification Module from Statistics Denmark

6. Methods Logistic Regression Analyses Adjusted analyses controlled for: Maternal psoriasis status Maternal age at birth Not adjusted for potential mediators, such as: obesity, stress, tonsillitis, etc. Cohort analyses (longitudinal data) and cross-sectional analyses (cross-sectional data at 11-year follow-up) were conducted Effect modification analyses Likelihood ratio tests were conducted, testing for interaction between the variables maternal psoriasis status and socioeconomic position For significant interaction test results, analyses stratified by maternal psoriasis status

7. Results Study Population 36,003 offspring were included in the population for analysis 34,793 without psoriasis 395 with psoriasis 815 missing data The mothers of offspring in the DNBC were mainly characterized by age at birth: 25-34 years education: medium to high labour market attachment: employed

8. Results Logistic Regression Analyses aData registered December 31st, the year prior to the child’s birth; bAdjusted for maternal psoriasis status; cAdjusted for maternal psoriasis status and maternal age at birth. * P <0.05; ** P <0.01; *** P <0.001.

9. Results Inverse associations between SEP and psoriasis Offspring in lowest category of maternal age at birth, had a 1.84 (95 % CI 1.35, 2.51) greater odds of psoriasis compared to reference Offspring with low maternal educational attainment had a 1.73 greater odds (95 % CI 1.30, 2.30) of psoriasis compared to reference No statistically significant increase in odds of offspring psoriasis observed for maternal labour market attachment Steep inverse social gradient in offspring psoriasis observed for equivalised household income

10. Discussion Main findings A steep inverse social gradient was observedfor maternal age at birth, maternal educational attainment (ISCED) and equivalised household income Additionally, these gradients in socioeconomic position exposures appeared to be consistent at baseline and 11-year follow-up (cohort and cross-sectional analyses)

11. Discussion Study limitations Outcome status misclassification Offspring psoriasis status based on maternally-reported questionnaire data Likely biased results towards null (misclassification with atopic dermatitis which has a positive social gradient) Potential differential loss to follow-up Mothers with low SEP might be less likely to participate at 11-year follow-up non-differential (by outcome status) unlikely to be mothers of children with psoriasis with higher SEP Potentially biases results towards the null

12. Discussion Interpretation Environmental exposures associated with socioeconomic position during early infancy and early childhood appear to be important determinants of paediatric-onset psoriasis Paediatric-onset psoriasis is more prevalent among those with a lower socioeconomic position Mediating factors are relevant to identify, to better target interventions and counselling for this high-risk population

13. What does this study add? This study is among the first to demonstrate a social gradient for paediatric-onset psoriasis in a large cohort population, indicating the potential for primary and secondary prevention Offspring with a low maternal socioeconomic position may be an especially vulnerable population at high risk of paediatric-onset psoriasis It may be important to consider the impact of a child’s socioeconomic position on their risk of developing paediatric-onset psoriasis

14. The research team From left to right: Jonathan Groot MScPH, Professor Anne-Marie Nybo Andersen MD PhD, Tilde Elkjær Tind Nielsen MSc, Christoffer Blegvad MD, and Professor Lone Skov MD PhDDMSci.

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