Conversely, alleles of <i>ABHD5</i> carrying point mutations associated with ichthyosis in humans failed to accelerate PNPLA1-mediated AcylCer biosynthesis.
Notably, topical application of epidermal lipids from wild-type onto Pnpla1-mutant mice promoted rebuilding of the corneocyte-bound lipid envelope, indicating that supplementation of ichthyotic skin with omega-O-acylceramides might be a therapeutic approach for the treatment of skin symptoms in individuals affected by omega-O-acylceramide deficiency.
Altogether, our results indicate that PNPLA1 is directly involved in acylceramide synthesis as a transacylase, and provide important insights into the molecular mechanisms of skin barrier formation and of ichthyosis pathogenesis.
Mutations in connexin 26 are linked to diseases including Vohwinkel syndrome, keratitis-ichthyosis deafness, and hystrix-like ichthyosis deafness syndromes, palmoplantar keratoderma with deafness, deafness with Clouston-like phenotype, and Bart-Pumphrey syndrome.
The phenotype of the HID (hystrix-like ichthyosis, deafness)/KID (keratitis, ichthyosis, deafness) syndrome is primarily characterized by skin changes.
In addition, whole exome sequencing approach also solved the genetics of some syndromic forms of PAI including IMAGe syndrome (<i>CDKN1C</i>), Irish traveler syndrome (<i>MCM4</i>), MIRAGE syndrome (<i>SAMD9</i>); and most recently a syndrome combining FGD with steroid-resistant nephrotic syndrome and ichthyosis caused by mutations in the gene for sphingosine-1-phosphate lyase 1 (<i>SGPL1</i>).
In 7 families with SRNS and facultative ichthyosis, adrenal insufficiency, immunodeficiency, and neurological defects, we identified 9 different recessive mutations in SGPL1, which encodes sphingosine-1-phosphate (S1P) lyase.
Self-improving collodion ichthyosis occurred in 8% of the cases (mostly TGM1 and ALOX12B mutations) but could not be predicted precisely from neonatal phenotype or genotype.
Ichthyoses lacked the epidermal differentiation and tight junction alterations of patients with AD (loricrin, filaggrin, and claudin 1) but showed characteristic alterations in lipid metabolism genes (ELOVL fatty acid elongase 3 and galanin), with parallel reductions in extracellular lipids and corneocyte compaction in all ichthyoses except epidermolytic ichthyosis, suggesting phenotypic variations.
The lack of filaggrin is associated with various cutaneous (<i>e.g. ichthyosis vulgaris</i>, allergic contact dermatitis) and non-cutaneous (<i>e.g.</i> diabetes, inflammatory conditions of the gastrointestinal tract) diseases and may be a result of genetic, immunological factors combined with environmental factors.
This mixed phenotype suggests the need for a better understanding of the possible role of filaggrin loss and AP1 transcription factor deficiency in ichthyoses and collodion membrane formation.