Discovery in genetic skin disease: the impact of high throughput genetic technologies

The novel high-frequency variant of TRPV3 p.A628T in East Asians showing faster sensitization in response to chemical agonists

TRPV3, a member of the thermosensitive Ca²⁺-permeable TRPV channel subfamily expressed in skin and sensory nerves, is also activated by chemical agonists such as 2-aminoethyl diphenylborinate (2-APB). Repetitive stimuli induce sensitization of TRPV3 activation, characterized by the cumulative increase in current amplitude and linearization of current-voltage relation (I/V curve). Through genomic analysis of various populations, we found non-rare TRPV3 mutation (p.A628T) in East Asian people with an allele frequency of 0.249 while 0.007 in Caucasian. Slope conductance of unitary channel was not different between WT and p.A628T. Whole-cell patch clamp study of wildtype TRPV3 (WT) and p.A628T overexpressed in HEK293T cells showed similar sensitization by the repetitive increase in temperature from 23 to 37 °C, while slightly higher sensitization to 43 °C in p.A628T. In contrast, the repetitive application of 2-APB (10 μM) or carvacrol (100 μM) induced faster sensitization in p.A628T than WT. However, 1 μM farnesyl pyrophosphate, an intrinsic lipid metabolite agonist, induced similar level of slow activations in WT and p.A628T. In Fura-2 microspectrofluorimetry, the 2-APB pulses induced a faster increase of [Ca²⁺]_c in p.A628T than WT. In terms of ionic selectivity of channels, WT and p.A628T showed similar Ca²⁺ permeability (P_Ca/P_Na) calculated from the reversal potential of I/V curves. Taken together, p.A628T shows faster sensitization to chemical agonists that are reflected as higher [Ca²⁺]_c signaling. Based on the intriguing pharmacological sensitivity, the physiological implications of p.A628T in the East Asian population require further investigation.

p63 is a key regulator of iRHOM2 signalling in the keratinocyte stress response

Hyperproliferative keratinocytes induced by trauma, hyperkeratosis and/or inflammation display molecular signatures similar to those of palmoplantar epidermis. Inherited gain-of-function mutations in RHBDF2 (encoding iRHOM2) are associated with a hyperproliferative palmoplantar keratoderma and squamous oesophageal cancer syndrome (termed TOC). In contrast, genetic ablation of rhbdf2 in mice leads to a thinning of the mammalian footpad, and reduces keratinocyte hyperproliferation and migration. Here, we report that iRHOM2 is a novel target gene of p63 and that both p63 and iRHOM2 differentially regulate cellular stress-associated signalling pathways in normal and hyperproliferative keratinocytes. We demonstrate that p63-iRHOM2 regulates cell survival and response to oxidative stress via modulation of SURVIVIN and Cytoglobin, respectively. Furthermore, the antioxidant compound Sulforaphane downregulates p63-iRHOM2 expression, leading to reduced proliferation, inflammation, survival and ROS production. These findings elucidate a novel p63-associated pathway that identifies iRHOM2 modulation as a potential therapeutic target to treat hyperproliferative skin disease and neoplasia.

Steroid sulfatase and filaggrin mutations in a boy with severe ichthyosis, elevated serum IgE level and moyamoya syndrome

X-linked ichthyosis (XLI) is a relatively common, recessive condition caused by mutations in the steroid sulfatase (STS) gene. Common loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and predispose individuals to atopic eczema. We report a case of a 6-year-old boy who presented with unusually severe XLI, an increased serum immunoglobulin E level (2120IU/ml) and moyamoya angiopathy. Whole-exome sequencing identified a gross deletion encompassing the STS in Xp22.31 and the p.K4022X FLG mutation. The deletion is at least 1.6Mb in size in the proband, based on real-time quantitative polymerase chain reaction results. No other genetic mutations related to ichthyosis, moyamoya or hyper-immunoglobulin E syndrome were detected. Furthermore, his mother's brothers suffered from mild XLI and only had a deletion encompassing the STS. Additionally, his father and older sister suffered from mild ichthyosis vulgaris and had the p.K4022X FLG mutation. We report the first case of XLI with concurrent moyamoya syndrome. Moreover, an IgE-mediated immune response may have triggered the moyamoya signaling cascade in this patient with ichthyosis. Furthermore, our study strengthens the hypothesis that filaggrin defects can synergize with an STS deficiency to exacerbate the ichthyosis phenotype in an ethnically diverse population.

Questioning the Clinical Utility of Exome Sequencing in Developing Countries

The availability of whole-exome sequencing has revolutionized the study of genetic disease in recent years, particularly in dermatology, where clinical phenotypes are readily recognized. As this technology becomes increasingly affordable and accessible, questions are emerging regarding the clinical and ethical responsibilities of physicians who determine variants underlying disease, especially with regard to children, for whom treatment may be warranted and clinical course improved based on a known genotype. These responsibilities are accentuated in the developing countries, which harbor most consanguineous populations and thus bear the brunt of monogenic genodermatoses. Although many genetic disorders are identified in these populations, limited educational and clinical infrastructure rarely offers opportunities to improve the course of disease. Here we report a genetic study that illustrates these challenges.

Advances and Applications of Ion Torrent Personal Genome Machine in Cutaneous Squamous Cell Carcinoma Reveal Novel Gene Mutations

The Ion Torrent Personal Genome Machine (Ion PGM) is a semiconductor-based sequencing technology that is high quality, scalable, and economic. Its applications include genomic sequencing, drug resistance testing, microbial characterization, and targeted sequencing in cancer studies. However, little is known about the application of Ion PGM in cutaneous squamous cell carcinoma (cSCC). We therefore investigated the utility and validity of Ion PGM in cSCC and also gained a better understanding of the underlying molecular biology of cSCC. We detected novel gene mutations (KDR, FGFR2, and EGFR) in two cSCC patients. Moreover, we validated these mutations by pyrosequencing and Sanger sequencing. Our results indicated that the mutation screen using Ion PGM is consistent with traditional sequencing methods. Notably, these identified mutations were present at significantly higher rates in high-risk cSCC. Our results demonstrate a method to detect targetable genes in high-risk cSCC, and suggest that Ion PGM may enable therapeutic decision-making and future potential targets for personalized therapies in cSCC.

Tylosis with oesophageal cancer: Diagnosis, management and molecular mechanisms

Tylosis (hyperkeratosis palmaris et plantaris) is characterised by focal thickening of the skin of the hands and feet and is associated with a very high lifetime risk of developing squamous cell carcinoma of the oesophagus. This risk has been calculated to be 95% at the age of 65 in one large family, however the frequency of the disorder in the general population is not known and is likely to be less than one in 1,000,000. Oesophageal lesions appear as small (2-5 mm), white, polyploid lesions dotted throughout the oesophagus and oral leukokeratosis has also been described. Although symptoms of oesophageal cancer can include dysphagia, odynophagia, anorexia and weight loss, there may be an absence of symptoms in early disease, highlighting the importance of endoscopic surveillance in these patients. Oesophageal cancer associated with tylosis usually presents in middle to late life (from mid-fifties onwards) and shows no earlier development than the sporadic form of the disease. Tylosis with oesophageal cancer is inherited as an autosomal dominant trait with complete penetrance of the cutaneous features, usually by 7 to 8 years of age but can present as late as puberty. Mutations in RHBDF2 located on 17q25.1 have recently been found to be causative. A diagnosis of tylosis with oesophageal cancer is made on the basis of a positive family history, characteristic clinical features, including cutaneous and oesophageal lesions, and genetic analysis for mutations in RHBDF2. The key management goal is surveillance for early detection and treatment of oesophageal dysplasia. Surveillance includes annual gastroscopy with biopsy of any suspicious lesion together with quadratic biopsies from the upper, middle and lower oesophagus. This is coupled with dietary and lifestyle modification advice and symptom education. Symptomatic management of the palmoplantar keratoderma includes regular application of emollients, specialist footwear and early treatment of fissures and super-added infection, particularly tinea pedis. More specific treatment for the thick skin is available in the form of oral retinoids, which are very effective but commonly produce side effects, including nasal excoriation and bleeding, hypercholesterolaemia, and abnormal liver function tests. Genetic counselling can be offered to patients and family members once a family history has been established. The prognosis of tylosis with oesophageal cancer is difficult to determine due to the limited number of affected individuals. In the last 40 years of surveillance, five out of six cases of squamous oesophageal cancer in the Liverpool family were detected endoscopically and were surgically removed. Four of five patients had stage 1 disease at presentation and remain alive and well more than 8 years later. This suggests that the presence of a screening program improves prognosis for these patients.