From a genetic perspective, the common psoriatic manifestations are complex or multifactorial diseases, manifesting due to a combination of genetic predisposition and external, environmental factors. The main risk factor for psoriasis vulgaris and psoriasis arthritis is an HLA C allele; further relevant risk factors could be found in the genes encoding the IL-23 receptor and the subunit of its ligand IL-12ß ( (Hüffmeier et al. 2009 (IL23R and IL12B)), a pathway that also plays a major role in the treatment of psoriasis. In addition, several copy number variants are known genetic risk factors in psoriasis, i.a. in the ß-defensin cluster on chromosome 8p23.1 and in the LCE3 gene cluster within a complex of many epidermally expressed genes (Hollox et al. 2008; Riveira-Munoz et al. 2011; Stuart, Huffmeier et al. 2012; Uebe et al. 2017). The groups of Prof. Dr. A. Reis and PD Dr. Ulrike Hüffmeierparticipate in large international genome-wide association studies (GWAS), where up to now more than 65 independent, reliably validated genetic risk factors for psoriasis and psoriatic arthritis have been identified in European populations (e.g. Hüffmeier, Uebe et al. 2010; Apel et al. 2013; Bowes et al. 2015; Strange et al. 2010; Stuart et al. 2015; Tsoi et al. 2012). In these studies, sequence variants (SNPs) and haplotypes in critical regions or functional candidates are systematically detected in association studies of very large case control studies. Associated genetic variants are functionally characterized in subsequent studies.