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.
OBJECTIVE: 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.

BACKGROUND: Pachyonychia congenita (PC) is a rare keratin disorder that typically presents with nail dystrophy and focal plantar keratoderma. We present seven cases of PC with transgrediens involvement of the dorsal feet.
OBJECTIVE: To document the extension of their disease to the dorsum of the feet in patients with mutation-confirmed PC, to report the natural history of PC with such transgrediens involvement, to generate hypotheses regarding aetiology, and to suggest prevention and treatment modalities.
METHODS: Genetically confirmed cases of PC with transgrediens foot involvement were verified through the International Pachyonychia Congenita Research Registry (IPCRR) and characterized via telephone survey and photography.
RESULTS: Seven patients with PC in the IPCRR were confirmed to have transgrediens lesions on the dorsal feet (six KRT6A mutations; one KRT16 mutation). Six cases had pre-existing nontransgrediens keratoderma and all cases reported standing, wearing shoes, foot moisture, and/or infection as exacerbating or predisposing factors. Improvement, reported in six cases, was attributed to use of antibiotics or gentian violet, or improved footwear.
CONCLUSIONS: Transgrediens involvement of the dorsal feet is a rare manifestation of mutation-confirmed PC and may be more common in patients who carry a KRT6A mutation. Trauma, friction, infection and wound healing may exacerbate or predispose toward transgrediens lesions. It remains to be proven whether transgrediens-associated infection is causal or represents a primary or secondary process. Patients with PC who develop transgrediens lesions may benefit from fungal and bacterial cultures, followed by appropriate antimicrobial treatments. Efforts to decrease skin friction and moisture may also improve and/or prevent transgrediens spread.

A 21-year-old man presented with hypertrophic nail dystrophy and subungual debris of all 20 nails, hyperkeratotic plaques on the heels of both feet, and oral leukokeratosis. He had an extensive family history of similar clinical findings. The patient\'s clinical presentation and history were consistent with pachyonychia congenita (PC), an autosomal dominant genodermatosis caused by mutations in the genes for keratin 6, K6a and K6b; keratin 16, K16; and keratin 17, K17.

A 46-year-old man had a cystic mass on the right side of his scalp. Histological examination revealed a cystic dermal nodule composed of relatively circumscribed lobules of proliferating squamous epithelium, with atypical mitoses and dyskeratotic cells of invasive structure, which was diagnosed as proliferating tricholemmal cystic carcinoma (PTCC). Most of the cyst was composed of thick layers of highly proliferating, atypical, dedifferentiated epithelium (dedifferentiated part), which was attached to a highly proliferative but mildly differentiated part. A completely differentiated, tricholemmal cyst (TC)-like part was also attached to the main cyst, which supports the idea of PTCC beginning in a pre-existing TC. The dedifferentiated and mildly differentiated parts exhibited a high frequency of proliferating cell nuclear antigen (PCNA)-positive cells both in the basal and the suprabasal layers, while PCNA staining was almost negative in the TC-like part. Expression of cytokeratin (CK)10 and CK16 suggested disturbed epidermal differentiation in dedifferentiated part, while TC-like part showed well-differentiated trichilemmal epithelium and the mildly differentiated part was in the middle of these two.