Supplementary Material for: Parental consanguinity and family history in relation to psoriasis and the role of sex: a case-control study

Introduction: Psoriasis is caused by an interplay between intrinsic and extrinsic factors. Parental consanguinity increases homozygosity in the genome of the offspring, which in turn increases disease risk. The association between parental consanguinity and psoriasis in the offspring remains unexplored. Therefore, this study sought to evaluate the association of parental consanguinity and family history with psoriasis in the offspring, and to determine whether sex modulates the aforementioned associations.
Methods: A case-control study enrolled adults aged 21 years and more. Psoriasis cases (n=139) diagnosed by dermatologists were enrolled from dermatology clinics. Controls (psoriasis-free subjects; n=278) were enrolled from workplaces. Study subjects reported information on parental consanguinity and family history of psoriasis. Logistic regression was applied to evaluate associations, and adjusted odds ratios (aOR) and 95% confidence intervals (CI) were estimated.
Results: Cases compared to controls were more likely to report parental consanguinity (59.7% vs. 35.6%; p <0.001) and family history of psoriasis (56.8% vs. 23.7%; p <0.001). Both parental consanguinity (aOR: 2.13, 95% CI: 1.29-3.50) and family history of psoriasis (aOR: 3.43, 95% CI: 2.07-5.67) were associated with increased odds of having psoriasis. The observed association between parental consanguinity and psoriasis differed according to sex (Pinteraction = 0.008), with parental consanguinity being associated with psoriasis among males (aOR: 5.96, 95% CI: 2.39-14.82), but not among females (aOR: 1.36, 95% CI: 0.75-2.49).
Conclusion: Psoriasis cases compared to controls were significantly more likely to report parental consanguinity and family history of psoriasis, with parental consanguinity being associated with psoriasis among males only.