Mary E. Schwartz

First-in-human Mutation-targeted siRNA Phase Ib Trial of an Inherited Skin Disorder

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 patients siRNA-treated foot appears sufficiently promising to warrant additional studies of siRNA in this and other dominant-negative skin diseases.

A review of the clinical phenotype of 254 patients with genetically confirmed pachyonychia congenita

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.

A Large Mutational Study in Pachyonychia Congenita

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.

Gene expression profiling in pachyonychia congenita skin

BACKGROUND 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. OBJECTIVE To better understand PC pathogenesis. METHODS 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. RESULTS 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. CONCLUSION 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.

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

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

Achieving Successful Delivery of Nucleic Acids to Skin: 6th Annual Meeting of the International Pachyonychia Congenita Consortium

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

Toward a Treatment for Pachyonychia Congenita: Report on the 7th Annual International Pachyonychia Congenita Consortium Meeting

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.

Expanding the Phenotypic Spectrum of Olmsted Syndrome

are of Slavic origin, suggesting an ancestral mutation propagated through Slavic migration to Northern Romania and Eastern Germany, where our patients are living. Nevertheless, the mutation affects a CpG dinucleotide, which has a high mutation rate from 5methylated CG to TG and its complementary pair CA, suggesting that it could also be recurrent. Altogether, we show that KS patients may harbor FERMT1 deep-intronic mutations, which are missed in targeted and whole-exome sequencing, and require RNA analysis or whole-genome sequencing. Our results argue against a genetic heterogeneity of KS.

Loss-of-Function Mutations in CAST Cause Peeling Skin, Leukonychia, Acral Punctate Keratoses, Cheilitis, and Knuckle Pads

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 patients with mutations in KRT6A have more extensive disease compared with patients who have mutations in KRT16.

Background  Pachyonychia congenita (PC) is an autosomal dominant, very rare keratin disorder caused by mutations in any of at least four genes (KRT6A, KRT6B, KRT16 or KRT17), which can lead to hypertrophic nail dystrophy and palmoplantar keratoderma, among other manifestations. Classically, patients with mutations in KRT6A and KRT16 have been grouped to the PC‐1 subtype (Jadassohn–Lewandowsky type) and KRT6B and KRT17 to PC‐2 (Jackson–Lawler type).