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Original Investigation
July 2016

Association of Psoriasis With the Risk for Type 2 Diabetes Mellitus and Obesity

Author Affiliations
  • 1Department of Dermato-Allergology, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark
  • 2The Danish Twin Registry, Institute of Regional Health Services Research, University of Southern Denmark, Odense
  • 3Odense Patient Data Explorative Network (OPEN), Odense University Hospital, Odense, Denmark
  • 4Department of Clinical Immunology, Naestved Hospital, Naestved, Denmark
  • 5Department of Dermatology, Bispebjerg Hospital, Copenhagen, Denmark
  • 6Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
JAMA Dermatol. 2016;152(7):761-767. doi:10.1001/jamadermatol.2015.6262
Abstract

Importance  Psoriasis has been shown to be associated with overweight and type 2 diabetes mellitus. The genetic association is unclear.

Objective  To examine the association among psoriasis, type 2 diabetes mellitus, and body mass index (BMI) (calculated as weight in kilograms divided by height in meters squared) in twins.

Design, Setting, and Participants  This cross-sectional, population-based twin study included 34 781 Danish twins, 20 to 71 years of age. Data from a questionnaire on psoriasis was validated against hospital discharge diagnoses of psoriasis and compared with hospital discharge diagnoses of type 2 diabetes mellitus and self-reported BMI. Data were collected in the spring of 2002. Data were analyzed from January 1 to October 31, 2014.

Main Outcomes and Measures  Crude and adjusted odds ratios (ORs) were calculated for psoriasis in relation to type 2 diabetes mellitus, increasing BMI, and obesity in the whole population of twins and in 449 psoriasis-discordant twins. Variance component analysis was used to measure genetic and nongenetic effects on the associations.

Results  Among the 34 781 questionnaire respondents, 33 588 with complete data were included in the study (15 443 men [46.0%]; 18 145 women [54.0%]; mean [SD] age, 44.5 [7.6] years). After multivariable adjustment, a significant association was found between psoriasis and type 2 diabetes mellitus (odds ratio [OR], 1.53; 95% CI, 1.03-2.27; P = .04) and between psoriasis and increasing BMI (OR, 1.81; 95% CI, 1.28-2.55; P = .001 in individuals with a BMI>35.0). Among psoriasis-discordant twin pairs, the association between psoriasis and obesity was diluted in monozygotic twins (OR, 1.43; 95% CI, 0.50-4.07; P = .50) relative to dizygotic twins (OR, 2.13; 95% CI, 1.03-4.39; P = .04). Variance decomposition showed that additive genetic factors accounted for 68% (95% CI, 60%-75%) of the variance in the susceptibility to psoriasis, for 73% (95% CI, 58%-83%) of the variance in susceptibility to type 2 diabetes mellitus, and for 74% (95% CI, 72%-76%) of the variance in BMI. The genetic correlation between psoriasis and type 2 diabetes mellitus was 0.13 (−0.06 to 0.31; P = .17); between psoriasis and BMI, 0.12 (0.08 to 0.19; P < .001). The environmental correlation between psoriasis and type 2 diabetes mellitus was 0.10 (−0.71 to 0.17; P = .63); between psoriasis and BMI, −0.05 (−0.14 to 0.04; P = .44).

Conclusions and Relevance  This study determines the contribution of genetic and environmental factors to the interaction between obesity, type 2 diabetes mellitus, and psoriasis. Psoriasis, type 2 diabetes mellitus, and obesity are also strongly associated in adults after taking key confounding factors, such as sex, age, and smoking, into account. Results indicate a common genetic etiology for psoriasis and obesity.

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