Patients with Congenital Ichthyosis and TGM1 Mutations Overexpress Other ARCI Genes in the Skin: Part of a Barrier Repair Response?

Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of monogenic skin disorders caused by mutations in any of >10 different genes, many of which are involved in epidermal synthesis of ω-O-acylceramides (acylCer), an essential precursor of the corneocyte lipid envelope that is also dependent on transglutaminase-1 for normal skin barrier formation.  We hypothesized that inactivating TGM1 mutations, the most common cause of ARCI, might lead to a compensatory overexpression of transcripts involved in barrier repair, including ARCI-causing genes. Using microarray we examined the global mRNA expression profile in skin biopsies from five ARCI-patients with TGM1 mutations and four healthy controls. There were a total of 602 differentially expressed genes (adjusted P<0.05). Gene ontology analysis showed enrichment of mRNA encoding proteins associated with biological pathways mainly involved in keratinocyte differentiation and adaptive/innate immune response. Moreover, among non-syndromic ARCI-causing genes, seven out of twelve were significantly increased (log2fold -change=0.98-2.05). Four genes causing syndromic ichthyosis and seven other genes involved in biosynthesis of fatty acyl-CoA and ceramides were also significantly affected. This study reveals upregulation of several ichthyosis-causing genes in the skin of patients with TGM1 mutations, indicating a compensatory induction of acylCer biosynthesis as a part of a barrier repair mechanism. Skin biopsies were obtained at the buttocks of ichthyosis patients with TGM1 mutations (n=5) and healthy controls (n=4).