New and Recurrent SERPINB7 Mutations in Seven Chinese Patients with Nagashima-Type Palmoplantar Keratosis

Nagashima-type palmoplantar keratosis palmoplantar keratoderma TO THE EDITOR Hereditary palmoplantar keratodermas (PPKs) consist of a heterogeneous group of hyperkeratotic disorders involving mainly the palms and the soles (Lucker et al., 1994Lucker G.P. Kerkhof P.C. Steijlen P.M. The hereditary palmoplantar keratoses: an updated review and classification.Br J Dermatol. 1994; 131: 1-14Crossref PubMed Scopus (103) Google Scholar). Nagashima-type palmoplantar keratosis (NPPK, MIM615598) was initially described in Japanese literature as a mild form of mal de Meleda (MIM248300), which is one of the diffuse autosomal-recessive PPKs (Nagashima, 1977Nagashima M. Palmoplantar keratoses.Jinrui Idengaku Shosho. 1977; 9 (in Japanese): 23-27Google Scholar). Later, similar cases were reported both in Japanese and English literature with a proposed name of NPPK (Mitsuhashi et al., 1989Mitsuhashi Y. Hashimoto I. Takahashi M. Meleda type keratosis palmoplantaris (Nagashima).Practical Dermatol. 1989; 11 (in Japanese): 297-300Google Scholar; Kabashima et al., 2008Kabashima K. Sakabe J. Tokura Y. et al.“Nagashima-type’’ keratosis as a novel entity in the palmoplantar keratoderma category.Arch Dermatol. 2008; 144: 375-379Crossref PubMed Scopus (44) Google Scholar). Genetic study of NPPK excluded SLURP1 mutations, which underlie mal de Meleda, indicating that NPPK was a genetically distinct entity (Kabashima et al., 2008Kabashima K. Sakabe J. Tokura Y. et al.“Nagashima-type’’ keratosis as a novel entity in the palmoplantar keratoderma category.Arch Dermatol. 2008; 144: 375-379Crossref PubMed Scopus (44) Google Scholar). More recently, Kubo et al., 2013Kubo A. Shiohama A. Sasaki T. et al.Mutations in SERPINB7, encoding a member of the serine protease inhibitor superfamily, cause Nagashima-type palmoplantar keratosis.Am J Hum Genet. 2013; 93: 945-956Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar identified biallelic loss-of-function mutations in the SERPINB7 gene, which encodes a member of the serine protease inhibitor (serpin) superfamily, as the genetic basis of NPPK. To date, all the reported patients with NPPK, to our knowledge, are of Japanese origin. Here, we report on seven unrelated Chinese patients with NPPK with four underlying SERPINB7 mutations, of which one is a recurrent variant (c.796C>T), whereas the other three, to our knowledge, are previously unreported. Seven sporadic patients (four males and three females) of Chinese Han ethnicity with diffuse, nonmutilating, and nonepidermolytic PPKs were enrolled. All the patients were unrelated from different provinces of China. No consanguinity or relevant family history was noted in all the cases. The clinical features of the seven patients were summarized in Table 1. In brief, all the patients presented with diffuse, reddish palmoplantar hyperkeratosis that extended to the waists, the Achilles tendons, and dorsum of the hands/feet (Figure 1a, b, and d), with the onset age ranging from birth to 4 years. Erythrokeratoderma, affecting elbows and knees, was seen in patients 1 and 6 (Figure 1c). Mild hyperhidrosis on the palms and soles, skin maceration, and recurrent tinea pedis were noted in most of the patients. The stratum corneum swelled and exhibited a whitish spongy appearance after the exposure to warm water for 5–10 min (Figure 1d). Histopathological changes are unremarkable, showing orthohyperkeratosis, acanthosis, and mild perivascular inflammatory infiltration of lymphocytes in the upper dermis.Table 1Summary of the clinical features and SERPINB7 mutations of the seven patientsPatientSexAge (years)Onset ageAllele 1Allele 2Clinical features in addition to PPKNucleotide changeAmino-acid changeNucleotide changeAmino-acid change1Female258 monthsc.796C>Tp.R266*c.796C>Tp.R266*Mild erythrokeratoderma on the elbows and knees2Male13At birthc.796C>Tp.R266*c.796C>Tp.R266*Tinea pedis, hyperhidrosis3Male176 monthsc.796C>Tp.R266*c.796C>Tp.R266*Tinea pedis, hyperhidrosis4Female246 monthsc.796C>Tp.R266*c.796C>Tp.R266*Tinea pedis, hyperhidrosis5Male111 yearc.796C>Tp.R266*c.650-653delCTGTp.S217Lfs*7Tinea pedis, hyperhidrosis6Female81 yearc.796C>Tp.R266*c.455G>Tp.G152V and predicted splicing alternationMild erythrokeratoderma affecting the elbows and knees, mild pruritus7Male304 yearsc.522-523insTp.V175Cfs*46c.522-523insTp.V175Cfs*46Onychomycosis and tinea pedis, hyperhidrosisAbbreviation: PPK, palmoplantar keratoderma. Open table in a new tab Abbreviation: PPK, palmoplantar keratoderma. Genomic DNA was extracted from peripheral blood of all seven patients and their family members, following their written informed consent. This study was approved by the institution review board in adherence to the Declaration of Helsinki Principles. Sanger sequencing was performed to screen mutations in SERPINB7, SLURP1, and AQP5. AQP5 codes for aquaporin 5 channel and was recently identified as the causative gene of PPK Bothnia-type (Blaydon et al., 2013Blaydon D.C. Lind L.K. Plagnol V. et al.Mutations in AQP5, encoding a water-channel protein, cause autosomal-dominant diffuse nonepidermolytic palmoplantar keratoderma.Am J Hum Genet. 2013; 93: 330-335Abstract Full Text Full Text PDF PubMed Scopus (65) Google Scholar; Cao et al., 2013Cao X. Yin J. Wang H. et al.Mutation in AQP5, encoding aquaporin 5, causes palmoplantar keratoderma Bothnia type.J Invest Dermatol. 2013; 134: 284-287Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar), an autosomal-dominant PPK sharing most clinical features with NPPK. No pathogenic mutations were found in SLURP1 or AQP5 in any of the seven patients, whereas four different mutations in SERPINB7 were detected, including one recurrent mutation (c.796C>T, p.R266*) found in 6 patients. Patients 1–4 were homozygous for c.796C>T mutation. In addition to the heterozygous mutation c.796C>T, patient 5 was found to have a heterozygous frameshift mutation c.650-653delCTGT (p.S217Lfs*7), and patient 6 harbored a heterozygous point mutation c.455G>T (p.G152V). The latter causes the change in the first nucleotide of exon 6, leading to an elimination of acceptor-splicing site of this exon (as predicted by BDGP Splice Site Prediction, with a drop in the splicing score from 0.89 to 0.42, see http://www.fruitfly.org/seq_tools/splice.html). Unfortunately, skin biopsy for mRNA verification was unacceptable for patient 6. Patient 7 was homozygous for a frameshift mutation c.522-523insT (p.V175Cfs*46) (Figure 1e and i). Parents of all patients (except patient 5, whose parents were unavailable) were heterozygous carriers of the corresponding mutations, consistent with an autosomal-recessive inheritance in all the families. Two of the mutations identified in this study, c.455G>T and c.796C>T, were found in single nucleotide polymorphism databases. According to the 1000 Genomes Project, c.455G>T (rs202182550) was present in a heterozygous form in 1 of 197 Chinese individuals, and c.796C>T (rs142859678) was found in a heterozygous manner in 6 of 197 Chinese individuals. Allele frequency of these two SNPs adds up to more than 0.017, and the estimated prevalence rate of NPPK is ∼3 in 10,000 in China. As mutation c.796C>T was highly prevalent in our patients (Kubo et al., 2013Kubo A. Shiohama A. Sasaki T. et al.Mutations in SERPINB7, encoding a member of the serine protease inhibitor superfamily, cause Nagashima-type palmoplantar keratosis.Am J Hum Genet. 2013; 93: 945-956Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar), we employed haplotype analysis in the 6 patients harboring mutation c.796C>T to determine whether this mutation was derived from one common ancestor or it represented a mutation hotspot. Ten SNPs that are highly polymorphic in Chinese populations adjacent to the mutation were chosen and genotyped by Sanger sequencing. Patients 1–4 shared identical homozygous alleles in all 10 SNPs, and patients 5 and 6 harbored all the alleles of the other four patients (Supplementary Table S1 online), suggesting that these six patients are likely to share a common mutant haplotype. Therefore, it is reasonable to infer that, instead of a mutation hotspot, c.796C>T was a founder mutation. Similar founder effect was also demonstrated in TGM5, in which a recurrent mutation c.337G>T, with an allele frequency of 0.015 in Northern Europeans, is commonly present in European patients with acral peeling skin syndrome (Pigors et al., 2012Pigors M. Kiritsi D. Cobzaru C. et al.TGM5 mutations impact epidermal differentiation in acral peeling skin syndrome.J Invest Dermatol. 2012; 132: 2422-2429Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar; van der Velden et al., 2012van der Velden J. Jonkman M.F. McLean W.H.I. et al.A recurrent mutation in the TGM5 gene in European patients with acral peeling skin syndrome.J Derma Sci. 2012; 65: 74-76Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar). Download .pdf (.03 MB) Help with pdf files Supplementary materials and methods SERPINB7 encodes a subtype of clade-B serpins which inhibit serine proteases and protect cells from protease-mediated damage (Silverman et al., 2004Silverman G.A. Whisstock J.C. Askew D.J. et al.Human clade B serpins (ov-serpins) belong to a cohort of evolutionarily dispersed intracellular proteinase inhibitor clades that protect cells from promiscuous proteolysis.Cell Mo Life Sci. 2004; 61: 301-325Crossref PubMed Scopus (154) Google Scholar). SERPINB7 was distributed in the epidermis throughout the body, especially in the stratum granulosum and upper part of the stratum corneum. Loss-of-function of SERPINB7 may induce overactivation of proteases specifically in NPPK skin lesions, resulting in protein degradation of keratinocytes, and facilitating water permeation into the stratum corneum (Kubo et al., 2013Kubo A. Shiohama A. Sasaki T. et al.Mutations in SERPINB7, encoding a member of the serine protease inhibitor superfamily, cause Nagashima-type palmoplantar keratosis.Am J Hum Genet. 2013; 93: 945-956Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar). All of the truncated proteins of SERPINB7 in our patients were predicted to lose the entire motif of the reactive site loop, which is located at amino acids 331–352 and crucial for its function (Kubo et al., 2013Kubo A. Shiohama A. Sasaki T. et al.Mutations in SERPINB7, encoding a member of the serine protease inhibitor superfamily, cause Nagashima-type palmoplantar keratosis.Am J Hum Genet. 2013; 93: 945-956Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar), leading to a complete absence of the protease inhibitory activity of SERPINB7. In conclusion, we ascertained seven Chinese individuals with NPPK and identified four causative mutations in SERPINB7, two of which were polymorphic present in normal Chinese individuals. NPPK was estimated to be one of the most common types of autosomal-recessive PPKs in China despite its delayed recognition. Moreover, we confirmed that the recurrent nonsense mutation c.796C>T, prevalent both in Chinese and Japanese NPPK patients, probably descended from the same ancestor. Finally, mutation screening of c.796C>T in SERPINB7 can serve as a cost-effective diagnostic strategy in the setting of Chinese and Japanese patients with diffuse, nonmutilating-inherited PPKs, but without distinctive clinical or histopathological features. We are grateful to the patients and family members who participated in this study. We thank Ming Yang Lee, Madelaine Niam, and Sindhu Subramaniam at University College London for the final proofreading. This work was supported by the National Natural Science Foundation of China (grant nos. 81201220 and 81271744). Supplementary material is linked to the online version of the paper at http://www.nature.com/jid