الفهرس 
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Abstract
Psoriasis is a common, chronic, relapsing/remitting, immunemediated
disease characterized by red, scaly papules and plaques with
a worldwide prevalence of 2–4%. The most common form of psoriasis
is plaque psoriasis. Other less common types of psoriasis also occur,
such as pustular, guttate, erythrodermic, inverse and psoriatic arthritis.
The most characteristic lesions consist of red, scaly sharply
demarcated, erythematous papules and plaques present particularly
over the extensor surfaces and the scalp.
The exact etiology of psoriasis is unknown, but evolving
evidence suggests that it is a complex disease caused by interaction of
multiple factors includes immunological, genetic and environmental
factors. It has been recognized as a systemic disorder associated with
various comorbidities.
Human CRNN gene is encoded on chromosome 1q21 where the
epidermal differentiation complex localized. CRNN is a 53-KDa
protein of 495 amino acids with a calcium-binding motif of about 90
residues at its N-terminus and a conserved consecutive repeat
sequence of 60 amino acids. Its structural characteristics are similar to
those of ―fused gene‖ family members of the epidermal differentiation
complex. In recent years, increasing evidence has implicated the role
of CRNN in a wide range of human squamous-cell epithelioma.
Cornulin, also called c1orf10 or SEP53, is a cornified squamous
epithelial protein. CRNN was initially discovered in esophageal cells.
Subsequent studies have shown that CRNN is also expressed in other
squamous cells and epithelial cells. It is located primarily in the upper
layers of differentiated squamous tissues and plays an important role epidermal differentiation. CRNN was considered as a marker of late
keratinocyte differentiation.
Psoriasis susceptibility 4 is a psoriasis susceptibility gene in the
chromosome 1q21 region. The 1q21 region harbors EDC. Altered
epidermal differentiation is an important hallmark of psoriatic skin;
therefore, the EDC genes have been considered psoriasis gene
candidate.