C. David Hansen

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.

The Phenotypic and Molecular Genetic Features of Pachyonychia Congenita

Pachyonychia congenita (PC) is an autosomal dominant genodermatosis caused by heterozygous mutations in any one of the genes encoding the differentiation-specific keratins K6a, K6b, K16, or K17. The main clinical features of the condition include painful and highly debilitating plantar keratoderma, hypertrophic nail dystrophy, oral leukokeratosis, and a variety of epidermal cysts. Although the condition has previously been subdivided into PC-1 and PC-2 subtypes, the phenotypic characterization of 1,000 mutation-verified PC patients enrolled in the International PC Research Registry, coordinated by the patient advocacy group PC Project, shows that there is considerable overlap between these subtypes. Thus, a new genotypic nomenclature is proposed, in which PC-6a represents a patient carrying a mutation in the K6a gene, etc. Although a rare disorder, PC represents a good model for therapy development, and international efforts are ongoing to develop and deliver siRNA, gene, correction, small molecule, and other strategies to treat this painful, disabling skin condition. The special relationship between PC Project and the PC research community has greatly accelerated the development pathway from gene identification to clinical trials in only a few years and represents a paradigm of hope for other orphan 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.

Androgen receptor expression patterns in Becker's nevi: An immunohistochemical study

BACKGROUND Beckers nevus (BN) is a hyperpigmented patch that traditionally presents on the upper torso in adolescent males. Previous studies have reported an association with increased androgen receptors (ARs) in lesional skin in men and women who have associated physical abnormalities. OBJECTIVE This study was conducted to assess the presence of ARs immunohistochemically in female patients with BN but no other physical abnormalities and compare this finding with BN in males and in normal skin. METHODS Biopsy specimens from Beckers nevi in 3 women and 3 men as well as normal skin in the 3 female subjects were stained with AR antibody, and the level of expression in various cutaneous structures was measured. RESULTS ARs were increased in dermal fibroblasts in Beckers nevi compared to that found in normal skin. LIMITATIONS The major limitation of the study was the small sample size. CONCLUSION In BN there is increased AR expression in dermal fibroblasts; immunohistochemical staining may aid in making the biopsy diagnosis.

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

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.