Pachyonychia Congenita

Keratin 6A, 6B, 6C, 16, 17 gene mutations
Autosomal dominant inheritance
Type 1 (Jadassohn–Lewandowsky) due to keratin 6a / 16 gene mutation leads to severe palmoplantar keratoderma and oral leukokeratosis
Type 2 (Jackson–Lawler) due to keratin 6b / 17 gene mutation leads to pilosebaceous cysts, neonatal teeth
Current classification system of paronychia congenita: -6a (~40%), -6b (~5–10%), -6c (<5%), -16 (~30%), -17 (~15–20%)

Ectodermal (nail bed, palmoplantar skin, pilosebaceous unit, oral mucosa, tooth) anomalies

Toenail dystrophy, focal keratoderma, plantar pain
- Keratin 6a gene mutation causes oral mucosa and nail disease
- Keratin 17 gene mutation causes pilosebaceous unit disease, steatocystoma multiplex
- Keratin 6c / 16 causes focal palmoplantar keratoderma
Wedge-shaped subungual hyperkeratosis (“omega” shape), fissures, frictional blisters, palmoplantar hyperhidrosis, paronychia, severe pain, follicular keratoses, angular cheilitis, oral leukokeratosis, natal teeth, hair abnormalities, steatocystomas, vellus hair cysts, hoarseness, respiratory tract obstruction

Pathology:

Cytoplasmic pallor and eosinophilic inclusions among superficial epidermal keratinocytes
- Perinuclear aggregation of abnormal keratin filaments, cytoplasm vacuolization
- Similar to white sponge nevus histology (due to keratin 4, 13 gene mutations)

Differential:

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