Identification of gene signatures and molecular mechanisms underlying the mutual exclusion between psoriasis and leprosy.

Leprosy and psoriasis rarely coexist, the specific molecular mechanisms underlying their mutual exclusion have not been extensively investigated. This study aimed to reveal the underlying mechanism responsible for the mutual exclusion between psoriasis and leprosy. We obtained leprosy and psoriasis data from ArrayExpress and GEO database. Differential expression analysis was conducted separately on the leprosy and psoriasis using DEseq2. Differentially expressed genes (DEGs) with opposite expression patterns in psoriasis and leprosy were identified, which could potentially involve in their mutual exclusion. Enrichment analysis was performed on these candidate mutually exclusive genes, and a protein-protein interaction (PPI) network was constructed to identify hub genes. The expression of these hub genes was further validated in an external dataset to obtain the critical mutually exclusive genes. Additionally, immune cell infiltration in psoriasis and leprosy was analyzed using single-sample gene set enrichment analysis (ssGSEA), and the correlation between critical mutually exclusive genes and immune cells was also examined. Finally, the expression pattern of critical mutually exclusive genes was evaluated in a single-cell transcriptome dataset. We identified 1098 DEGs in the leprosy dataset and 3839 DEGs in the psoriasis dataset. 48 candidate mutually exclusive genes were identified by taking the intersection. Enrichment analysis revealed that these genes were involved in cholesterol metabolism pathways. Through PPI network analysis, we identified APOE, CYP27A1, FADS1, and SOAT1 as hub genes. APOE, CYP27A1, and SOAT1 were subsequently validated as critical mutually exclusive genes on both internal and external datasets. Analysis of immune cell infiltration indicated higher abundance of 16 immune cell types in psoriasis and leprosy compared to normal controls. The abundance of 6 immune cell types in psoriasis and leprosy positively correlated with the expression levels of APOE and CYP27A1. Single-cell data analysis demonstrated that critical mutually exclusive genes were predominantly expressed in Schwann cells and fibroblasts. This study identified APOE, CYP27A1, and SOAT1 as critical mutually exclusive genes. Cholesterol metabolism pathway illustrated the possible mechanism of the inverse association of psoriasis and leprosy. The findings of this study provide a basis for identifying mechanisms and therapeutic targets for psoriasis.

Insight into evolution of a giant congenital nevomelanocytic nevus over 14 years.

Giant congenital nevomelanocytic nevus (GCNN) is a rare variant of congenital melanocytic nevus measuring >20 cm in size that often has a garment-like distribution. Regular follow up is recommended because of a risk of melanoma transformation of 4.6%. We report a 14-year-old boy with gradual regression of giant congenital melanocytic nevus over the left upper limb, chest, back and axilla, whom we have followed-up since birth. At birth, a hyperpigmented jet-black patch without hair was present over the left side of torso and upper limb including palms and nails. Follow up at the ages of 1, 5, 11 and 14 years showed progressive spontaneous regression of the nevus resulting in shiny atrophic skin, diffuse hypopigmentation, lentigo-like macules, nodules and arthrogryphosis of affected areas. Histopathology of the lesions on follow-up revealed absence of pigmented nevus cells in the regressing areas and thickened sclerotic collagen bundles.