Psoriasis is a chronic, inflammatory dermatosis that affects approximately 2% of the population, making it is one of the most common human skin diseases. Clinically, it is characterized by dry, reddish, thickened patches of the skin that are covered with silvery-gray scales. These patches are found on the scalp, elbows, knees, hands, feet, and/or lower back. These patches may be referred to as papules or plaques. They may be intensely itchy (pruritis) or sore. In some cases, patients may experience abnormalities affecting the fingernails, toenails, and the soft tissues inside the mouth. This disease has many clinical forms, vulgaris is the most common, and the pustular psoriasis is the less one. In this variety, the pustules are the predominant lessons, and it may be localized or generalized. Moreover, a substantial proportion of patients with psoriasis may develop a form of inflammatory arthritis known as psoriatic arthritis which contributes significantly to patient's disease burden with physical disability, pain and further reduction in quality of life. . The severity of psoriasis varies from case to case. Psoriasis may be classified as mild, moderate or severe depending upon the amount of skin involved and the effect on an individual's quality of life. The usual age of onset of psoriasis is between 15 and 30 years, although it can present at any age.
Psoriasis is a lifelong and progressive condition. There is currently no cure but various treatments can help to control the symptoms. These treatments include topical formulations, systemic therapies, phototherapies, and combination therapies.
The immunopathogenetic mechanisms in psoriasis development of this disease are not well known. It seems that psoriasis is a genetic disease of keratinocyte hyperproliferation mediated by T lymphocytes. A large number of triggering or aggravating environmental factors have been identified in subjects genetically predisposed to psoriasis such as bacterial (streptococci) and viral (HIV) infections, certain drugs, stress, alcoholism, and smoking.
It is well known that psoriasis is consistent with a multifactorial pattern of inheritance. However, family history is present in approximately one-third of cases. Psoriasis is genetically heterogeneous disease. The strongest genetic determinant of psoriasis identified to date lies within the class 1 region of the multiple histocompatibility locus antigen cluster on chromosome 6p21, particularly HLA-Cw6 allele which is highly associated with the disease.