Data from a gene expression array shows that palmoplantar postulosis (PPP) and palmoplantar pustular psoriasis (PPPP) are genetically similar diseases but different from psoriasis vulgaris, the most common form of psoriasis. Study results were published in PLOS One, in a paper titled “Based on molecular profiling of gene expression, palmoplantar pustolosis and palmoplantar pustular psoriasis are highly related diseases that appear to be distinct from psoriasis vulgaris.”
PPP and PPPP are skin diseases that localize specifically to the palms and soles, skin regions that contrast markedly with others of the human body, lacking hair and sebaceous glands and showing an increased thickness of the skin’s outermost layer. The two diseases manifest in different ways, with PPP being defined as a chronic skin disease that causes crops of sterile pustules with erythema and, at times, scaling on soles and palms, and PPPP being identified as a variant of plaque psoriasis present on palms and soles with the presence of sterile pustules.
Nonetheless, some patients have intermediate morphologies, with coexistence of psoriasis and PPP-associated descriptions, raising the question of whether these patients have both diseases or different clinical presentations of the same disease.
To address this question, researchers from Innovaderm Research and Rockefeller University collected skin biopsies from the palms or soles of normal subjects and patients with PPP, PPPP or psoriasis vulgaris, and then analyzed them using a gene expression microarray. Results revealed that PPP and PPPP samples clustered together and could not be differentiated based on their gene expression pattern, suggesting that they are not clinically distinct entities. However, consistent with the morphological differences of skin from the palms and soles, and skin from elsewhere on the body, PPP/PPPP gene expression was strikingly different from both normal skin and psoriasis vulgaris.
In addition, when PPP/PPPP skin samples were compared with psoriasis vulgaris or with normal skin from the palms and soles, several genes involved in neural pathways, such as GPRIN and ADAM23, were found to be expressed in higher levels in PPP/PPPP samples and mainly localized to keratinocytes, the predominant cell type in the skin’s outermost layer. This suggests that these proteins could represent new therapeutic targets for PPP/PPPP.
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