Increased risk of major depressive disorder among probands with psoriasis and unaffected siblings: a nationwide population-based study

Background: Previous studies have shown that patients with psoriasis have a higher risk of depression. However, the risk of major depressive disorder (MDD) among unaffected siblings of psoriasis probands remains unknown. This study aimed to investigate the risk of MDD among probands with psoriasis and unaffected siblings. Methods: We selected subjects from the National Health Insurance Research Database (NHIRD) in Taiwan. Subjects were followed up from 01 January 1996 until a diagnosis of MDD, death or 31 December 2011. The Breslow–Cox model was used to calculate the adjusted relative risk (aRR). Results: This study included 1094 probands with psoriasis, 1202 unaffected siblings and 4808 matched controls. Overall, 11.9% of the psoriasis probands (n = 130) and 2.5% of the unaffected siblings (n = 30) developed MDD, as compared with 1.1% of the controls (n = 52). Compared with controls, probands with psoriasis and unaffected siblings had aRRs of 10.60 [95% confidence interval (CI): 7.73–14.52] and 2.17 (95% CI: 1.44–3.28), respectively, for MDD. Conclusions: Probands with psoriasis and unaffected siblings have an increased risk of subsequently developing MDD. Further studies are needed to investigate the shared familial mechanisms underlying psoriasis and MDD.