Fine mapping of the disseminated superficial porokeratosis locus to a 2.7 Mb region at 18p11.3

Splicing mutation in MVK is a cause of porokeratosis of Mibelli

Porokeratosis is a chronic skin disorder characterized by the presence of patches with elevated, thick, keratotic borders, with histological cornoid lamella. Classic porokeratosis of Mibelli (PM) frequently appears in childhood with a risk of malignant transformation. Disseminated superficial actinic porokeratosis (DSAP) is the most common subtype of porokeratosis with genetic heterogeneities, and mevalonate kinase gene (MVK) mutations have been identified in minor portion of DSAP families of Chinese origin. To confirm the previous findings about MVK mutations in DSAP patients and test MVK's role(s) in PM development, we performed genomic sequence analysis for 3 DSAP families and 1 PM family of Chinese origin. We identified a splicing mutation of MVK gene, designated as c.1039+1G>A, in the PM family. No MVK mutations were found in three DSAP families. Sequence analysis for complementary DNA templates from PM lesions of all patients revealed a mutation at splice donor site of intron 10, designated as c.1039+1G>A, leading to the splicing defect and termination codon 52 amino acids after exon 10. Although no MVK mutations in DSAP patients were found as reported previously, we identified MVK simultaneously responsible for PM development.

Identification of an interstitial 18p11.32-p11.31 duplication including the EMILIN2 gene in a family with porokeratosis of Mibelli

Porokeratosis is a rare disease of epidermal keratinization characterized by the histopathological feature of the cornoid lamella, a column of tightly fitted parakeratocytic cells, whose etiology is still unclear. Porokeratosis of Mibelli is a subtype of porokeratosis presenting a single plaque or a small number of plaques of variable size located unilaterally on limbs. It frequently appears in childhood and occurs with a higher incidence in males. Cytogenetic analyses were performed in all members of the family on lesioned and uninvolved skin. An array-CGH analysis was also performed utilizing the Human Genome CGH Microarray Kit G3 400 with 5.3 KB overall median probe spacing. Gene expression was performed on skin fibroblasts. In this study, we describe a Caucasian healthy 4-year-old child and his father showing features of porokeratosis of Mibelli. Array-CGH analysis revealed an interstitial 429.5 Kb duplication of chromosome 18p11.32-p11.3 containing four genes, namely: SMCHD1, EMILIN2, LPIN2, and MYOM1 both in patient and his father. EMILIN2 resulted overexpressed on skin fibroblasts. Also other members of this family, without evident signs of porokeratosis, carried the same duplication. Among these genes, we focused our attention on elastin microfibril interfacer 2 (EMILIN2) gene. Apoptosis plays a fundamental role in maintaining epidermal homeostasis, balancing keratinocytes proliferation, and forming the stratum corneum. EMILIN2 is known to trigger the apoptosis of different cell lines negatively affecting cell survival. It is expressed in the skin. We could speculate that the duplication and overexpression of EMILIN2 cause an abnormal apoptosis of epidermal keratinocytes and alter the process of keratinization, even if other epigenetic and genetic factors could also be involved. Our results could contribute to a better understanding of the pathogenesis of porokeratosis of Mibelli.

Identification of a locus (DSP2) for disseminated superficial porokeratosis at chromosome 12q21.2-24.21

Porokeratosis is a rare disorder of epidermal keratinization that is characterized by the presence of a border called the cornoid lamella. Disseminated superficial porokeratosis (DSP) is a subtype of porokeratosis, which is inherited as an autosomal trait. The first locus for DSP was localized to chromosome 18p11.3, but no causative gene has yet been identified. In this study, we recruited and analysed a large six-generation Chinese family with autosomal dominant DSP. The genome-wide screening identified a maximum two-point LOD score of 3.06 at θ = 0.00 with the microsatellite marker D12S78. Fine mapping and haplotype analysis defined a critical region of 38 Mb between D12S326 and D12S79 on chromosome 12q21.2-24.21, which is a probable second locus identified for DSP (DSP2). We sequenced 50 candidate genes in this region, but no causative mutation was found. This study provides a map location for isolation of a gene causing DSP.