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Callus samples from the ball and the arch of the foot, collected on tape circles, were compared by shotgun proteomic profiling. Pachyonychia congenita subjects were sampled who exhibited a mutation in KRT6A, KRT6B, KRT6C, KRT16 or KRT17, and the proteins were digested and analyzed by tandem mass spectrometry. In comparison with samples from unaffected control subjects, those from subjects with KRT6A or KRT16 mutations displayed the most differences in profile from normal, while those from subjects with KRT6C or KRT17 mutations showed few differences from normal. The profiles from subjects with KRT6B mutations were intermediate in protein profile differences. Degree of departure from the normal profile could be estimated by expression of numerous proteins in callus from the ball of the foot that were consistently different. By contrast, the protein profile from the arch of the foot was hardly affected. The results provide a foundation for noninvasive monitoring of the efficacy of treatments with quantitative assessment of departure from the normal phenotype. Significance Pachyonychia congenita is an orphan disease in which the connection between the basic defect (keratin mutation) and debilitating symptoms (severe plantar pain) is poorly understood. Present work addresses the degree to which the protein profile is altered in the epidermis where the severe pain originates. The results indicate that the mutated keratins differ greatly in the degree to which they elicit perturbations in protein profile. In those cases with markedly altered protein levels, monitoring the callus profile may provide an objective measure of treatment efficacy.

Pachyonychia congenita (PC) is a cutaneous disorder primarily characterized by nail dystrophy and painful palmoplantar keratoderma. PC is caused by mutations in KRT6A, KRT6B, KRT6C, KRT16, and KRT17, a set of keratin genes expressed in the nail bed, palmoplantar epidermis, oral mucosal epithelium, hair follicle and sweat gland. RNA-seq analysis revealed that all PC-associated keratins (except for Krt6c that does exist in the mouse genome) are expressed in the mouse enamel organ. We further demonstrated that these keratins are produced by ameloblasts and are incorporated into mature human enamel. Using genetic and intraoral examination data from 573 adults and 449 children, we identified several missense polymorphisms in KRT6A, KRT6B and KRT6C that lead to a higher risk for dental caries. Structural analysis of teeth from a PC patient carrying a p.Asn171Lys substitution in keratin-6a (K6a) revealed disruption of enamel rod sheaths resulting in altered rod shape and distribution. Finally, this PC-associated substitution as well as more frequent caries-associated SNPs, found in two of the KRT6 genes, that result in p.Ser143Asn substitution (rs28538343 in KRT6B and rs151117600 in KRT6C), alter the assembly of K6 filaments in ameloblast-like cells. These results identify a new set of keratins involved in tooth enamel formation, distinguish novel susceptibility loci for tooth decay and reveal additional clinical features of pachyonychia congenita.

Pachyonychia congenita (PC) is a rare autosomal dominant genetic skin disorder due to a mutation in any one of the five keratin genes, KRT6A, KRT6B, KRT6C, KRT16, or KRT17. The main features are palmoplantar keratoderma, plantar pain, and nail dystrophy. Cysts of various types, follicular hyperkeratosis, oral leukokeratosis, hyperhidrosis, and natal teeth may also be present. Four unrelated Indian families presented with a clinical diagnosis of PC. This was confirmed by genetic testing; mutations in KRT17 were identified in all affected individuals.

Biobanks are increasingly powerful tools used in translational research, and disease advocacy organizations (DAOs) are making their presence known as research drivers and partners. We examined DAO approaches to biobanking to inform how the enterprise of biobanking can grow and become even more impactful in human health. In this commentary, we outline overarching approaches from successful DAO biobanks. These lessons learned suggest principles that can create a more participant-centric approach and illustrate the key roles DAOs can play as partners in research initiatives. DAO approaches to biobanking for translational research include the following: be outcome driven; forge alliances that are unexpected—build bridges to enhance translation; come ready for success; be nimble, flexible, and adaptable; and remember that people matter. Each of these principles led to particular practices that have increased the translational impact of biobank collections. The research practices discussed can inform partnerships in all sectors going forward.

Pachyonychia congenita (PC) is a cutaneous disorder primarily characterized by nail dystrophy and painful palmoplantar keratoderma. PC is caused by mutations in KRT6A, KRT6B, KRT6C, KRT16, and KRT17, a set of keratin genes expressed in the nail bed, palmoplantar epidermis, oral mucosal epithelium, hair follicle and sweat gland. RNA-seq analysis revealed that all PC-associated keratins (except for Krt6c that does exist in the mouse genome) are expressed in the mouse enamel organ. We further demonstrated that these keratins are produced by ameloblasts and are incorporated into mature human enamel. Using genetic and intraoral examination data from 573 adults and 449 children, we identified several missense polymorphisms in KRT6A, KRT6B and KRT6C that lead to a higher risk for dental caries. Structural analysis of teeth from a PC patient carrying a p.Asn171Lys substitution in keratin-6a (K6a) revealed disruption of enamel rod sheaths resulting in altered rod shape and distribution. Finally, this PC-associated substitution as well as more frequent caries-associated SNPs, found in two of the KRT6 genes, that result in p.Ser143Asn substitution (rs28538343 in KRT6B and rs151117600 in KRT6C), alter the assembly of K6 filaments in ameloblast-like cells. These results identify a new set of keratins involved in tooth enamel formation, distinguish novel susceptibility loci for tooth decay and reveal additional clinical features of pachyonychia congenita., Author summary Tooth decay, more commonly known as dental cavities, is the most common chronic disease worldwide, both in children and in adults. It consists in the destruction of tooth enamel, the outer layer of the teeth, by acid-producing bacteria. Enamel is the hardest tissue in the body, comprised of 96% minerals. However, it contains a small fraction of proteins that is important for its resistance to mechanical stress and decay. Here we show that this protein fraction contains a set of structural proteins (K6a, K6b, K6c, K16 and K17) that belong to the keratin family and are present specifically in the skin of the palms and soles, as well as in nails. We further show that common genetic mutations that affect the composition of these proteins lead to an increased number of cavities. Rare mutations in these keratins lead to a human disease called pachyonychia congenita (PC) and characterized by severe nail malformations and lesions in the skin of the palms and soles. Analysis of wisdom teeth from one of these patients showed that their enamel exhibited structural defects. These results demonstrate that these keratins are important components of tooth enamel and that common genetic variants in the genes that encode them influence tooth decay risk in the general population.

Calpastatin is an endogenous specific inhibitor of calpain, a calcium-dependent cysteine protease. Here we show that loss-of-function mutations in calpastatin (CAST) are the genetic causes of an autosomal-recessive condition characterized by generalized peeling skin, leukonychia, acral punctate keratoses, cheilitis, and knuckle pads, which we propose to be given the acronym PLACK syndrome. In affected individuals with PLACK syndrome from three families of different ethnicities, we identified homozygous mutations (c.607dup, c.424A>T, and c.1750delG) in CAST, all of which were predicted to encode truncated proteins (p.Ile203Asnfs∗8, p.Lys142∗, and p.Val584Trpfs∗37). Immunohistochemistry shows that staining of calpastatin is reduced in skin from affected individuals. Transmission electron microscopy revealed widening of intercellular spaces with chromatin condensation and margination in the upper stratum spinosum in lesional skin, suggesting impaired intercellular adhesion as well as keratinocyte apoptosis. A significant increase of apoptotic keratinocytes was also observed in TUNEL assays. In vitro studies utilizing siRNA-mediated CAST knockdown revealed a role for calpastatin in keratinocyte adhesion. In summary, we describe PLACK syndrome, as a clinical entity of defective epidermal adhesion, caused by loss-of-function mutations in CAST.

Pachyonychia congenita (PC) is a skin disorder resulting from mutations in keratin (K) proteins including K6a, K6b, K16, and K17. One of the major symptoms is painful plantar keratoderma. The pathogenic sequelae resulting from the keratin mutations remain unclear.To better understand PC pathogenesis.RNA profiling was performed on biopsies taken from PC-involved and uninvolved plantar skin of seven genotyped PC patients (two K6a, one K6b, three K16, and one K17) as well as from control volunteers. Protein profiling was generated from tape-stripping samples.A comparison of PC-involved skin biopsies to adjacent uninvolved plantar skin identified 112 differentially-expressed mRNAs common to patient groups harboring K6 (i.e., both K6a and K6b) and K16 mutations. Among these mRNAs, 25 encode structural proteins including keratins, small proline-rich and late cornified envelope proteins, 20 are related to metabolism and 16 encode proteases, peptidases, and their inhibitors including kallikrein-related peptidases (KLKs), and serine protease inhibitors (SERPINs). mRNAs were also identified to be differentially expressed only in K6 (81) or K16 (141) patient samples. Furthermore, 13 mRNAs were identified that may be involved in pain including nociception and neuropathy. Protein profiling, comparing three K6a plantar tape-stripping samples to non-PC controls, showed changes in the PC corneocytes similar, but not identical, to the mRNA analysis.Many differentially-expressed genes identified in PC-involved skin encode components critical for skin barrier homeostasis including keratinocyte proliferation, differentiation, cornification, and desquamation. The profiling data provide a foundation for unraveling the pathogenesis of PC and identifying targets for developing effective PC therapeutics.

Protein adhesins are an important type of surface structure, and are components of some Gram-negative bacterial outer membranes, such as Pseudomonas fluorescens. The LapA adhesin is a major surface protein on this bacterium, which is required for irreversible adhesion and the initiation of biofilm formation. Atomic force microscopy (AFM) was used to characterize surface structures of P. fluorescens Pf0-1. The wild-type and three genetically modified strains were studied, namely a strain consisting of a single cross-over knockout mutation disrupting the lapA gene, a strain consisting of a single cross-over knockout mutation disrupting the lapB gene, (LapA is maintained in the cytoplasm and not transported to the cell surface), and lapG (LapA is unable to be cleaved from the cell surface). AFM data was modeled using the Alexander de Gennes (A-dG) relation for steric repulsion. We calculated the equilibrium layer thickness of the surface structures as well as spacing between adhesins. The wild-type strain and the lapA and lapB mutants all showed similar spacing for surface proteins. The strain lacking LapG had the smallest spacing between molecules. This suggests that the absence of the LapG protease allowed the LapA protein to accumulate, thus decreasing the overall molecular spacing of the protein on the bacterial surface compared to the wild-type strain. We found that the lapG mutant strain of P. fluorescens behaved like a classical polymer brush, in which the spacing between molecules was very small (3.3 nm), which would allow intermolecular interactions between protein units. Recent work has shown that the lapG mutant has greater adhesion and biofilm formation than the wild-type, lapA, and lapB strains, and exhibits stiffer conformation of LapA due to higher protein density and aggregation. Taken together, our results and these recent studies support the finding that LapA adhesin conformation is related to irreversible bacterial

Summary This is a report of the research presented at the 11th Annual Meeting of the International Pachyonychia Congenita Consortium, held on 6 May 2014 in Albuquerque, NM, U.S.A. This year's meeting was divided into five corners concerning pachyonychia congenita (PC) research: (i) ‘PC Pathogenesis Cornered’, an overview of recent keratin research, for PC and other skin disorders; (ii) ‘From All Corners of …’, an outline of other genetic disorders that we can learn from; (iii) ‘Fighting For Our Corner’, an outline of National Institutes of Health/National Institute of Arthritis and Musculoskeletal and Skin Diseases programmes and U.S. funding opportunities applicable to rare skin disorders; (iv) ‘The PC Corner’, focusing on recent clinical studies related to PC; and (v) ‘Clinical Corners: Turning the Corner?’, an update on ongoing PC clinical trials.

Background Pachyonychia congenita (PC) is a rare autosomal dominant keratinizing disorder characterized by severe, painful, palmoplantar keratoderma and nail dystrophy, often accompanied by oral leucokeratosis, cysts and follicular keratosis. It is caused by mutations in one of five keratin genes: KRT6A, KRT6B, KRT6C, KRT16 or KRT17. Objectives To identify mutations in 84 new families with a clinical diagnosis of PC, recruited by the International Pachyonychia Congenita Research Registry during the last few years. Methods Genomic DNA isolated from saliva or peripheral blood leucocytes was amplified using primers specific for the PC-associated keratin genes and polymerase chain reaction products were directly sequenced. Results Mutations were identified in 84 families in the PC-associated keratin genes, comprising 46 distinct keratin mutations. Fourteen were previously unreported mutations, bringing the total number of different keratin mutations associated with PC to 105. Conclusions By identifying mutations in KRT6A, KRT6B, KRT6C, KRT16 or KRT17, this study has confirmed, at the molecular level, the clinical diagnosis of PC in these families.

The International Pachyonychia Congenita Consortium (IPCC) was founded in 2004 in Park City, Utah, USA. Its goal is to find a cure for pachyonychia congenita, a rare keratinizing disorder. From February 14th–17th, 2013, the group convened in Park City for their tenth annual meeting. The 2013 meeting focused on how to best move forward with clinical trials and on learning from work in other scientific areas, with an emphasis on understanding mechanisms of pain and hyperkeratosis. Considerable time was spent on discussing the best way to move forward with development of new treatments and how to obtain or develop tools that can measure treatment outcomes in PC.

A rare disease like pachyonychia congenita (PC) poses barriers to the patient, medical professional, and scientist. The patient has challenges connecting to information, the medical professional has challenges connecting to patient experience, and the scientist has challenges connecting to

Pseudomonas fluorescence Pf0-1 requires the large repeat protein LapA for stable surface attachment. This study presents direct evidence that LapA is a cell-surface-localized adhesin. Atomic force microscopy (AFM) revealed a significant 2-fold reduction in adhesion force for mutants lacking the LapA protein on the cell surface compared to the wild-type strain. Deletion of lapG, a gene encoding a periplasmic cysteine protease that functions to release LapA from the cell surface, resulted in a 2-fold increase in the force of adhesion. Three-dimensional structured illumination microscopy (3D-SIM) revealed the presence of the LapA protein on the cell surface, consistent with its role as an adhesin. The protein is only visualized in the cytoplasm for a mutant of the ABC transporter responsible for translocating LapA to the cell surface. Together, these data highlight the power of combining the use of AFM and 3D-SIM with genetic studies to demonstrate that LapA, a member of a large group of RTX-like repeat proteins, is a cell-surface adhesin. © 2012 Institut Pasteur.

The International Pachyonychia Congenita Consortium (IPCC) is a group of physicians and scientists who have agreed to work together to develop therapeutics for the rare skin disorder pachyonychia congenita (PC). Each IPCC meeting is devoted to the most pressing issues related to developing PC therapeutics and to reach consensus on directions to achieve realistic goals. A list of IPCC members can be found on the organization’s website (http://www.pachyonychia.org), and details of the oral presentations at this year’s annual meeting are listed in Supplementary Table 1 online.

Pachyonychia congenita (PC) is a rare autosomal dominant skin disorder characterized predominantly by nail dystrophy and painful palmoplantar keratoderma. Additional clinical features include oral leukokeratosis, follicular keratosis, and cysts (steatocysts and pilosebaceous cysts). PC is due to heterozygous mutations in one of four keratin genes, namely, KRT6A, KRT6B, KRT16, or KRT17. Here, we report genetic analysis of 90 new families with PC in which we identified mutations in KRT6A, KRT6B, KRT16, or KRT17, thereby confirming their clinical diagnosis. A total of 21 previously unreported and 22 known mutations were found. Approximately half of the kindreds had mutations in KRT6A (52%), 28% had mutations in KRT16, 17% in KRT17, and 3% of families had mutations in KRT6B. Most of the mutations were heterozygous missense or small in-frame insertion/deletion mutations occurring within one of the helix boundary motif regions of the keratin polypeptide. More unusual mutations included heterozygous splice site mutations, nonsense mutations, and a 1-bp insertion mutation, leading to a frameshift and premature termination codon. This study, together with previously reported mutations, identifies mutation hotspot codons that may be useful in the development of personalized medicine for PC.

Pachyonychia congenita (PC) is a rare autosomal dominant skin disorder characterized predominantly by hypertrophic nail dystrophy, oral leukokeratosis, and painful palmoplantar keratoderma. It is associated with a mutation in one of five keratin genes, KRT6A, KRT6B, KRT6C, KRT16, or KRT17. The International PC Research Registry (IPCRR) confirms that as of January 2014 there have been 547 cases of PC genetically confirmed. It is estimated that there are between 2000 and 10,000 cases of PC in the world. However, the exact prevalence of PC is not yet established. We report a case of PC-K6a, p.Arg164Pro, in a 40-year-old man. Initially he was diagnosed with onychomycosis and was treated with systemic antifungals. This is the first genetically confirmed case of PC in the Czech Republic.

The rare skin disorder pachyonychia congenita (PC) is an autosomal dominant syndrome that includes a disabling plantar keratoderma for which no satisfactory treatment is currently available. We have completed a phase Ib clinical trial for treatment of PC utilizing the first short-interfering RNA (siRNA)-based therapeutic for skin. This siRNA, called TD101, specifically and potently targets the keratin 6a (K6a) N171K mutant mRNA without affecting wild-type K6a mRNA. The safety and efficacy of TD101 was tested in a single-patient 17-week, prospective, double-blind, split-body, vehicle-controlled, dose-escalation trial. Randomly assigned solutions of TD101 or vehicle control were injected in symmetric plantar calluses on opposite feet. No adverse events occurred during the trial or in the 3-month washout period. Subjective patient assessment and physician clinical efficacy measures revealed regression of callus on the siRNA-treated, but not on the vehicle-treated foot. This trial represents the first time that siRNA has been used in a clinical setting to target a mutant gene or a genetic disorder, and the first use of siRNA in human skin. The callus regression seen on the patient's siRNA-treated foot appears sufficiently promising to warrant additional studies of siRNA in this and other dominant-negative skin diseases.

The 2009 Annual Meeting of the International Pachyonychia Congenita Consortium (IPCC)* centered on the need to develop patient-friendly tech-nologies to effectively and efficiently deliver nucleic acids to skin. The IPCC is a group of physicians and scientists who have agreed to work together to develop therapeutics for the rare skin disorder pachyonychia congenita (PC) (a list of IPCC members can be found at http://www.pachyonychia.org). Each year’s IPCC meeting is devoted to the most pressing issues related to devel-oping PC therapeutics and to identify-ing future directions toward achieving realistic goals. The consortium fully recognizes and expects that research success in this realm will be of imme-diate benefit not only to patients with PC but also to those suffering from other skin disorders.The 2009 meeting addressed the dif-ficulty of delivering nucleic acids to skin. The impetus for this topic was the recent phase Ib pachyonychia congenita clinical trial using a mutation-specific small interfering RNA (siRNA), TD101. The side-by-side, dose-escalation toxicity trial of intralesional injections of this mutation-specific siRNA exhib-ited no toxicity at the higher doses, and a clear clinical response was observed in the siRNA-treated site, but not in the site injected with vehicle alone (Leachman

IMPORTANCE Nail dystrophy in early childhood often suggests a diagnosis of pachyonychia congenita (PC). No previous investigation has focused on the early signs of PC and the natural course of the disease. OBJECTIVES To determine the course of pediatric PC, correlate the disease course with the clinical appearance and specific gene mutations, and assess the effect of pediatric PC on quality of life. DESIGN, SETTING, AND PARTICIPANTS One hundred one patients or families with genetically confirmed PC from the International Pachyonychia Congenita Research Registry who completed a survey on the general clinical features of PC and an auxiliary questionnaire on the clinical presentation and quality-of-life issues related to pediatric PC. EXPOSURE Individuals with pachyonychia congenita. MAIN OUTCOMES AND MEASURES Completion of both surveys. RESULTS At birth, toenail changes were present in 47.5% of patients; fingernail changes in 40.6%; and plantar keratoderma in 6.9%. By 5 years of age, these 3 key manifestations were found in 81.2%, 74.2%, and 75.3%, respectively, of individuals with genotype-confirmed PC. The correct diagnosis was made during the first year of life in 26.7% of patients despite the presence of toenail dystrophy in more than 65.3%. Clinical differences that distinguished PC subtypes included (1) later onset and less frequent occurrence of nail dystrophy and keratoderma in PC-K6b, PC-K6c, and PC-K16; (2) concurrent fingernail and toenail thickening in PC-K6a and PC-K17; (3) more palmar keratoderma in PC-K16; (4) cysts primarily in PC-K17 and follicular hyperkeratoses primarily in PC-K6a; (5) hoarseness and/or oral leukokeratoses in the first year of life most often in PC-K6a; and (6) natal teeth exclusively in PC-K17. Among pediatric patients, PC affected the social interactions and function of adolescents most profoundly. CONCLUSIONS AND RELEVANCE Among patients with a detectable mutation, PC manifests with nail thickening and plantar keratoderma before school age in more than three-quarters of affected children, allowing early diagnosis. The highly visible nail changes and painful plantar thickening exert a psychosocial effect on most affected adolescents. Phenotype-genotype correlations in children with PC validate the new classification based on the affected gene.

Background Pachyonychia congenita (PC) is a group of autosomal dominant keratinizing disorders caused by a mutation in one of 4 keratin genes. Previous classification schemes have relied on data from case series and case reports. Most patients in these reports were not genetically tested for PC. Objective We sought to clarify the prevalence of clinical features associated with PC. Methods We surveyed 254 individuals with confirmed keratin mutations regarding their experience with clinical findings associated with PC. Statistical comparison of the groups by keratin mutation was performed using logistic regression analysis. Results Although the onset of clinical symptoms varied considerably among our patients, a diagnostic triad of toenail thickening, plantar keratoderma, and plantar pain was reported by 97% of patients with PC by age 10 years. Plantar pain had the most profound impact on quality of life. Other clinical findings reported by our patients included fingernail dystrophy, oral leukokeratosis, palmar keratoderma, follicular hyperkeratosis, hyperhidrosis, cysts, hoarseness, and natal teeth. We observed a higher likelihood of oral leukokeratosis in individuals harboring KRT6A mutations, and a strong association of natal teeth and cysts in carriers of a KRT17 mutation. Most keratin subgroups expressed a mixed constellation of findings historically reported as PC-1 and PC-2. Limitations Data were obtained through questionnaires, not by direct examination. Patients were self- or physician-referred. Conclusions We propose a new classification for PC based on the specific keratin gene affected to help clinicians improve their diagnostic and prognostic accuracy, correct spurious associations, and improve therapeutic development.

Pachyonychia congenita (PC) is a rare, autosomal dominant keratin disorder caused by mutations in four genes (KRT6A, KRT6B, KRT16, or KRT17). The International PC Research Registry is a database with information on patients’ symptoms as well as genotypes. We sought to describe the heterogeneity of clinical symptoms and to investigate possible genotype–phenotype correlations in patients with two types of K16 mutations, p.Asn125 and p.Arg127, causing the PC-16 subtype of PC. We found that clinical symptoms depended on the type of amino-acid substitution. Patients with p.Asn125Asp and p.Arg127Pro mutations exhibited more severe disease than patients carrying p.Asn125Ser and p.Arg127Cys mutations in terms of age of onset of symptoms, extent of nail involvement, and impact on daily quality of life. We speculate that amino-acid substitutions causing larger, more disruptive changes to the K16 protein structure, such as a change in amino-acid charge in the p.Asn125Asp mutation or a bulky proline substitution in the p.Arg127Pro mutation, may also lead to more severe disease phenotypes. The variation in phenotypes seen with different substitutions at the same mutation site suggests a genotype–phenotype correlation. Knowledge of the exact gene defect is likely to assist in predicting disease prognosis and clinical management.

Homozygous Dominant Missense Mutation in Keratin 17 Leads to Alopecia in Addition to Severe Pachyonychia Congenita

These Symposium Proceedings summarize current clinical, therapeutic, and scientific challenges associated with developing effective treatments for pachyonychia congenita (PC). The impetus for these papers was the First International Pachyonychia Congenita Symposium, held on February 12–16, 2004, at the Yarrow Hotel in Park City, Utah. This symposium was sponsored by The Pachyonychia Congenita Fund (Pachyonychia Congenita Project/PC Project), a USA public charity founded in November 2003, which supports clinical and research activities related to the treatment of pachyonychia congenita. The goal of this symposium was to gather thought leaders, expert clinicians and scientists to explore approaches to the treatment and eventual cure for the disorder. As reflected in these Symposium Proceedings, the major topics of presentations included our most current understanding of the clinical and histologic features, therapeutic approaches, and the molecular genetics of the disease. In addition, ‘‘special topics’’ sessions focused on the most practical and efficient approaches to developing an eventual cure for PC, including discussions of the most useful model systems and genetic and pharmacologic approaches. Finally, the difficulty of initiating clinical trials and developing therapeutics for rare disorders of the skin was discussed at considerable length, with an emphasis on maximizing the relationship between academia and industry in this effort. All participants in this symposium were encouraged to critically evaluate options, and the roundtable discussion format permitted a productive and frequently lively exchange of ideas and information. Sancy Leachman, Patti Champine, Mary Schwartz, and Jan Schwartz organized the symposium, which opened with a series of lectures by Irwin McLean, Leonard Milstone, Alfred Lewin, Markus Landthaler, Mario Capecchi, Olga Igoucheva, and Roger Kaspar. These lectures focused on potential gene therapy technologies that could be applied to PC. The technologies that were considered included siRNA, ribozymes, triplex oligonucleotides, homologous recombination techniques, RNA lassos, and other oligonucleotidemediated gene repair techniques. The RNA-mediated technologies would aim to decrease the intracellular levels of the affected keratin and would have the potential advantages of being highly specific for the mutated RNA. These techniques would also have a transient, and thus reversible, character. The primary disadvantage to the RNA-based approach is that it would likely require ongoing repetitive administration in order to be effective. The gene correction therapies utilizing homologous recombination, triplexforming oligonucleotides, or other oligonucleotide-mediated repair techniques have the advantage of offering a more permanent correction of the mutated keratin, but are also less feasible in the short-term because of the difficulty in getting an adequate number of cells corrected in vivo. The problem of delivering these types of gene therapy agents to the nails and hyperkeratotic skin of PC patients was discussed in a lecture by Bhaskar Thyagarajan. It was concluded by the conference attendees that delivery will be one of the major obstacles to overcome in the treatment of PC. The next session included a thorough examination of the clinical, histologic, and molecular genetic features of PC led by Philip Fleckman, Frances Smith, and Maurice van Steensel. It has now become clear through mutation screening of PC patients that the clinical phenotype of PC is somewhat variable and that the two major categories, PC-1 and PC-2, can be discriminated by mutations in K6a or K16 for PC-1 and K6b or K17 for PC-2. The clinical and genetic discussions ultimately led to the development of a questionnaire designed to facilitate further elucidation of genotype-phenotype relationships in PC. This questionnaire has now been completed by 57 participants in the newly formed PC Registry, and data from these questionnaires are reported in Leachman et al in this issue. The final session of the conference focused on the potential model systems available to advance our understanding of the pathogenesis of PC as well as serve as preclinical models for therapeutic agents. Dennis Roop and Pauline Wong described the currently available cellular and mouse models. Consensus was reached by the group that a PC mouse model would be an extremely valuable tool for both basic and pre-clinical investigation. Various approaches to the development of this model were discussed, and it was felt that one of the best strategies would be to create a mutant K6a knock-in to try to replicate the dominant-negative effect of the mutation. It was also decided that models containing only a minor modification of the mouse gene as well as a ‘‘humanized’’ model containing human regulatory regions should be attempted. An important outcome of the meeting was the development of the International Pachyonychia Congenita Consortium (IPCC), a collaborative team of clinicians and scientists interested in pursuing PC care and research. A major accomplishment of the IPCC has been the development of a collaborative research strategy in which PC research projects are integrated to maximize efficiency and minimize cost by sharing key resources and reagents. The IPCC has identified several important gaps in our understanding of PC and in the approaches that have been taken toward devel