Work

A novel NCSTN missense mutation in the signal peptide domain causes hidradenitis suppurativa, which has features characteristic of an autoinflammatory keratinization disease

Year: 2019

Type: article

Abstract: Dear Editor, NCSTN encodes nicastrin, one of the three subunits of γ‐secretase, a transmembrane endoprotease complex that catalyses the cleavage of many transmembrane proteins including Notch receptors.1 In 2010, mutations in genes encoding γ‐secretase subunits (NCSTN, PSENEN and PSEN1) were reported in patients with hidradenitis suppurativa (HS).2 Elevated tumour necrosis factor‐α and interleukin (IL)‐10 levels in patients with HS with NCSTN mutations have been found,1 although other reports found no elevation3 or found decreases.4 We investigated a three‐generation Japanese family with HS with autosomal dominant inheritance. The patient was a 42‐year‐old man with many erosions, scars, comedones and cysts on the face, neck, trunk, armpits, buttocks and extremities (Fig. 1a). A biopsy sample from the buttock showed clear evidence of hyperkeratosis of the follicular epithelium and the occlusion and dilatation of follicles by keratin plug formation (Fig. 1b, c). Interestingly, he had had severe renal failure with unknown aetiology and had received haemodialysis from his twenties. Clinicopathological and genetic features. (a) Widespread scars, erosions and cysts are seen on the back, buttocks and thighs. (b, c) Haematoxylin and eosin staining of a sample of affected skin shows hyperkeratosis and hyperplasia of the follicular epithelium [scale bars: 500 μm (b), 200 μm (c)]. (d) A schematic of the NCSTN domain structure. The patient's mutation is marked by a black arrow. (e–h) Immunohistochemistry of the epidermis in normal control skin and patient skin with anti‐nicastrin [ab45425; Abcam, Cambridge, U.K., scale bars: 50 μm (e) and 20 μm (f)]; anti‐Notch1 [ab52627; Abcam, (g)] and anti‐Notch2 [ab8926; Abcam) (h)] antibodies [(g), (h) scale bars: 50 μm]. (i) The intensity of the staining for nicastrin (Nica) and Notch1 and Notch2 proteins was evaluated in the patient and in 10 control samples using ImageJ software (National Institutes of Health, Bethesda, MD, U.S.A.). TM, transmembrane domain; Pt, patient; cont, control. Additional figures depicting sequencing and pedigree are available on request from the authors. Serum biochemistry showed normal IL‐1β (< 10 pg mL−1) and mildly elevated IL‐18 (449 pg mL−1, normal range: < 211 pg mL−1). A cousin and an aunt of the patient also had haemodialysis because of the complication of chronic renal disease. This study was performed according to the principles of the Declaration of Helsinki and was approved by the Ethics Committee of the Nagoya University Graduate School of Medicine. Written informed consent was obtained from all participants. Whole‐exome sequencing of peripheral blood genomic DNA from the patient revealed a nonsynonymous heterozygous mutation in NCSTN [c.97G>A (p.Gly33Arg)], which was confirmed by Sanger sequencing (Fig. 1d). Subsequent sequencing of PSENEN and PSEN1 revealed no mutations. The c.97G>A mutation does not appear in the Human Genetic Variation Database, which includes 1208 exome datasets from Japanese controls (http://www.hgvd.genome.med.kyoto-u.ac.jp/index.html) or in the gnomAD Database (http://gnomad.broadinstitute.org/), which includes data for 123 136 whole‐exomes and 15 496 whole‐genomes. In silico analysis with PolyPhen‐2 (http://genetics.bwh.harvard.edu/pph2/), SIFT (https://sift.bii.a-star.edu.sg/), PROVEAN (http://provean.jcvi.org/) and MutationTaster (http://www.mutationtaster.org/) predict the mutation to be ‘damaging’. We did not identify potentially pathogenic mutations in any other genes implicated in HS. Additionally, we found no potential mutations in any genes related to renal failure in the exome dataset. Sequencing of DNA samples from five members of the family revealed co‐segregation of the c.97G>A mutation with the disease phenotype of HS. Immunohistochemistry revealed the staining intensity of nicastrin to be lower in the patient's skin than in control skin samples (Fig. 1e, f). Further, immunoreactivities of Notch1 and Notch2 were lower in the patient's lesional skin than in control skin samples (Fig. 1g–i). Several facts support the pathogenicity of p.Gly33Arg. Firstly, the mutation was completely segregated in the skin phenotypes of five individuals in the pedigree. Secondly, the mutation affects a residue that is highly conserved among seven different species (confirmed by MutationTaster). Thirdly, protein function prediction browsers attribute very high scores for damage from the mutation. Finally, the mutation lies on the signal peptide region of nicastrin. The present substitution is located at the last amino acid of the estimated signal peptide. We deployed two useful tools, SignalP (http://www.cbs.dtu.dk/services/SignalP/) and PrediSi (http://www.predisi.de/), to predict the cleavage site of the signal peptides. Both tools determined that the mutant nicastrin might have aberrantly located signal peptide cleavage sites. Moreover, our expression analyses by immunohistochemistry suggested decreased nicastrin expression and the dysfunction of Notch1 and Notch2 signalling. These findings are consistent with immunohistochemical analyses of previous reports.5 Notably, three of six patients with HS in this pedigree showed severe chronic renal failure. It is known that people with long‐term skin inflammation may be at risk for renal disease because of chronic inflammation.6 Krueger and Brunner reported the effect of IL‐17 on inflammatory pathways in cells of various types, including in keratinocytes, as well as in epithelial cells of the kidney.6 Additionally, IL‐17 upregulation has been demonstrated in HS.7 Chronic skin inflammation, such as seen with IL‐17 upregulation, because of HS may be a risk factor for renal disease. Recently, we proposed the new umbrella term ‘autoinflammatory keratinization diseases’ (AIKDs) to encompass inflammatory keratinization disorders with autoinflammatory mechanisms.8 De Vita and McGonagle reported HS as an AIKD.7 They proposed that histological psoriasiform hyperplasia of the interfollicular epidermis with subepidermal inflammatory infiltrates might be interpreted as an inflammation‐driven process basically identical to the one that is evident at the terminal follicles in HS.7 Interestingly, many lesions of follicular hyperkeratosis and hyperplasia of the follicular epithelium were observed in this patient (Fig. 1b, c). Thus, our findings clearly demonstrate that HS caused by NCSTN mutations has features characteristic of AIKD. Funding sources: this work was supported by funding from the Japan Agency for Medical Research and Development JP18ek0109295h0002 and 18ek0109281h0002 to M.A. It was also supported by a Grant‐in‐Aid for Scientific Research (B) 18H02832 to M.A. and by a Grant‐in‐Aid for Young Scientists 18K16058 to T.T. from the Japan Society for the Promotion of Science. Conflicts of interest: none to declare.

Source: British Journal of Dermatology

DOI: 10.1111/bjd.18445