At least 30% of psoriasis cases correspond to family forms (presence of family history) involving a genetic predisposition. Indeed, there is not a single gene responsible for psoriasis disease but rather a set of genes. The genetic variants associated with psoriasis disease are located in the genes involved in immunity, which is the cause of an immune system disorder.
To note : in the case of familial forms, if one of the two parents is affected, the risk for the child to suffer from the disease varies from 5 to 10%.
According to genetic linkage studies, PSORS1 is the primary locus of psoriasis susceptibility: it is responsible for 35 to 50% of psoriasis heritability. The PSORS1 region also contains the CDSN gene which codes for the corneodesmosin, a desmosomal protein involved in the cohesion and desquamation of keratinocytes. The locus is associated with an early onset of the disease.
The other loci highlighted by genetic linkage studies are PSORS2 and PSORS4. The most probable susceptibility gene in PSORS2 is CARD14. It codes for an activator of the nuclear factor-κB (NF-κB) and contains variants associated with both rare and common forms of psoriasis. As for the PSORS4 locus, it contains the genes of the "late cornified envelope" (LCE), which code for proteins of the horny layer involved in terminal epidermal differentiation.
Thanks to scientific advancements, various genetic analysis methods such as GWAS (Genome Wide Association Study) or CGH Microarray, over 80 loci have been associated with a high risk of psoriasis.
Thus, psoriasis is a disease for which genetic factors account for 70% of the disease's susceptibility. Understanding the genetic aspect of psoriasis is crucial, as it enables the development of effective treatments.