Psoriasis (psoriasis vulgaris; PV) is a chronic inflammatory dermatosis that affects approximately 2% of the population. It is characterized by red, scaly skin patches that are usually found on the scalp, elbows, and knees, and may be associated with severe arthritis. The lesions are caused by abnormal keratinocyte proliferation and infiltration of inflammatory cells into the dermis and epidermis. The usual age of onset of psoriasis is between 15 and 30 years, although it can present at any age (summary by Matthews et al., 1996). Generalized pustular psoriasis (GPP) is a life-threatening disease characterized by sudden, repeated episodes of high-grade fever, generalized rash, and disseminated pustules, with hyperleukocytosis and elevated serum levels of C-reactive protein (123260) (summary by Marrakchi et al., 2011). GPP often presents in patients with existing or prior psoriasis vulgaris; however, GPP can develop without a history of PV (Sugiura et al., 2013). Palmoplantar pustulosis and acrodermatitis continua of Hallopeau represent acral forms of pustular psoriasis that have historically been grouped with GPP (summary by Setta-Kaffetzi et al., 2013). Nestle et al. (2009) provided a detailed review of the pathogenesis and genetics of psoriasis. Genetic Heterogeneity of Psoriasis and Psoriasis Susceptibility PSORS2 (602723) is caused by mutation in the CARD14 gene (607211) on chromosome 17q25, and PSORS14 (614204) is caused by mutation in the IL36RN gene (605507) on chromosome 2q14. Psoriasis susceptibility loci include PSORS1 on 6p21.3; PSORS3 (601454) on 4q; PSORS4 on 1q21; PSORS5 (604316) on 3q21; PSORS6 (605364) on 19p; PSORS7 (605606) on 1p; PSORS8 (610707) on 16q; PSORS9 (607857) on 4q31; PSORS10 (612410) on 18p11; PSORS11 (612599) on 5q31-q33; PSORS12 (612950) on 20q13; PSORS13 (614070), conferred by variation in the TRAF3IP2 gene (607043) on 6q21; and PSORS15 (616106), conferred by variation in the AP1S3 gene (615781) on 2q36. An additional putative psoriasis candidate locus has been reported on 20p (Nair et al., 1997).

Epidermolysis bullosa simplex (EBS) is characterized by fragility of the skin (and mucosal epithelia in some instances) that results in non-scarring blisters and erosions caused by minor mechanical trauma. EBS is distinguished from other types of epidermolysis bullosa (EB) or non-EB skin fragility syndromes by the location of the blistering in relation to the dermal-epidermal junction. In EBS, blistering occurs within basal keratinocytes. The severity of blistering ranges from limited to hands and feet to widespread involvement. Additional features can include hyperkeratosis of the palms and soles (keratoderma), nail dystrophy, milia, and hyper- and/or hypopigmentation. Rare EBS subtypes have been associated with additional clinical features including pyloric atresia, muscular dystrophy, cardiomyopathy, and/or nephropathy.