188 Profiling of the transcriptome in hidradenitis suppurativa: A case-control sample

188 Profiling of the transcriptome in hidradenitis suppurativa: A case-control sample A Vossen, A Stubbs, M van Doorn, K van Straalen, H van der Zee and E Prens 1 Dermatology, Erasmus MC, Rotterdam the Netherlands, Rotterdam, Netherlands and 2 Bioinformatics, Erasmus MC, Rotterdam the Netherlands, Rotterdam, Netherlands Hidradenitis suppurativa (HS) is a chronic, inflammatory skin disease. The pathogenesis is poorly understood and is thought to originate in the follicular infundibulum due to unknown etiology. To increase our understanding of HS, we used RNA-sequencing to investigate the transcriptome of lesional HS skin. Polyadenylated RNA-derived cDNAs from HS subjects (n1⁄422) and skin samples from healthy volunteers (n1⁄410) were sequenced on a Affymetrix sequencing platform. Data analysis identified 1,827 genes (of which 1,279 unique known genes) as being differentially expressed with an at least 2-fold change and FDR <0.01. Comparison of the 32 samples revealed marked differences in genes associated with agranulocyte adhesion and diapedesis, the IL-17 A and F, IL-21, and the antimicrobial peptides especially S100A7, S100A8 and HBD-2. Furthermore inflammasome pathway activation in keratinocytes was demonstrated by upregulation of caspases (CASP 1, CASP 5) and members of the NLR-family. Consistent with the hypothesis, IL-1 family cytokines (IL-1a, IL-17, IL-36A) were significantly elevated in lesional skin homogenates. This was further confirmed by immunohistochemistry for IL-1. Most interestingly, a dominant plasma cell and B cell signatures were most evident in lesional skin. This study confirms, now at the RNA-seq level, previous findings on the expression of abovementioned cytokines in HS lesions. In addition, our RNA-seq data were compared with two existing data sets from psoriasis and revealed similarities in a total of 47 genes, including UBIAD1, SPRR2B/3, IL-19 and several AMPs. This study for the first time demonstrates, at the RNA-seq level, activation of inflammatory pathways and genes associated with comorbidities in HS. We postulate that IL-1a originating from keratinocytes of the infundibulum initiate an inflammatory cascade that further activates IL-1b, IL-8, and IL-17A, leading to a predominant neutrophil influx causing a significant disease burden. 189 A novel PLEC isoform modifies the phenotype in epidermolysis bullosa simplex KB Gostynska, H Lemmink, J Bremer, H Pas, M Nijenhuis, P van den Akker, R Sinke, M Jonkman and M Pasmooij 1 Dermatology, Univeristy of Groningen, University Medical Centre Groningen, Groningen, Netherlands and 2 Genetics, University of Groningen, University Medical Centre Groningen, Groningen, Netherlands Epidermolysis bullosa simplex (EBS) is caused by autosomal recessive and dominant mutations in PLEC in 8% of all cases. In humans, eight distinct plectin isoforms have been identified arising from tissue specific translation, differing in the first exon. Additionally, alternative splicing of exon 31 results in a rodless plectin variant, seen in patients affected with EBS with muscular dystrophy (EBS-MD). Complete absence of plectin leads to a severe phenotype with generalized blistering and pyloric atresia (EBS-PA), and early mortality. Here we studied the phenotype-genotype correlation in a patient with clinical EBS. A 17-year old girl had mild acral blistering present since early childhood with progressive muscular dystrophy and cardiomyopathy. Immunofluorescence antigen mapping and electron microscopy pointed both to a plectin deficiency. Plectin expression was reduced in skin and DNA analysis identified a homozygous deletion of 22 base pairs in intron 8 of PLEC. RT-PCR revealed intron retention ending in a premature termination codon predicting complete loss of plectin expression. However, an alternative splice site upstream was identified in patient and control samples. The mRNA transcript produced by the use of the alternative splice site resulted in an internally truncated protein and could explain plectin skin expression and lack of pyloric atresia in our patient. This transcript was also present in samples of healthy control keratinocytes, myocardium and striated muscle. We describe physiological alternative splicing of exon 8, resulting in a novel in frame plectin isoform. Our data demonstrate that plectin is not only alternatively spliced in exon 1 and 31, but also in exon 8 in healthy individuals. A severe EBS phenotype in our patient was most likely averted due to the production of the slightly shorter, functional protein.