title: Pachyonychia Congenita (K16) with Unusual Features and Good Response to Acitretin.
abstract: BACKGROUND
  Pachyonychia congenita (PC) is a rare autosomal dominant disease whose main clinical features include hypertrophic onychodystrophy and palmoplantar keratoderma. The new classification is based on genetic variants with mutations in keratin KRT6A, KRT6B, KRT6C, KRT16, KRT17, and an unknown mutation. Here, we present a case of PC with unusual clinical and histological features and a favorable response to oral acitretin.
  
  
  METHODS
  A 49-year-old male presented with diffuse and striate palmoplantar keratoderma, thickened nails, knuckle pads, and pseudoainhum. Histology showed compact hyperkeratosis, prominent irregular acanthosis, and extensive epidermolytic hyperkeratosis, suggestive of Vörner's palmoplantar keratoderma. However, keratin 9 and 1 were not mutated, and full exome sequencing showed heterozygous missense mutation in type I keratin K16.
  
  
  CONCLUSIONS
  To our knowledge, epidermolytic hyperkeratosis has not been previously described with PC. Our patient had an excellent response, maintained over the last 5 years, to a low dose of acitretin. We wish to emphasize the crucial role of whole exome sequencing in establishing the correct diagnosis.
authors.affiliation: Department of Medicine, Faculty of Medicine, Kuwait University, Jabriya, Kuwait.
authors.forename: Fahad
authors.initials: F
authors.lastname: Almutawa
authors.affiliation: Division of Dermatology, McGill University Health Centre, Montreal, Que., Canada.
authors.forename: Thusanth
authors.initials: T
authors.lastname: Thusaringam
authors.affiliation: Department of Pathology, McGill University Health Centre, Montreal, Que., Canada.
authors.forename: Kevin
authors.initials: K
authors.lastname: Watters
authors.affiliation: Department of Pediatrics, McGill University Health Centre, Montreal, Que., Canada ; Department of Human Genetics, McGill University Health Centre, Montreal, Que., Canada.
authors.forename: Tenzin
authors.initials: T
authors.lastname: Gayden
authors.affiliation: Department of Pediatrics, McGill University Health Centre, Montreal, Que., Canada ; Department of Human Genetics, McGill University Health Centre, Montreal, Que., Canada.
authors.forename: Nada
authors.initials: N
authors.lastname: Jabado
authors.affiliation: Division of Dermatology, McGill University Health Centre, Montreal, Que., Canada.
authors.forename: Denis
authors.initials: D
authors.lastname: Sasseville
keywords: Exome sequencing; Pachyonychia congenita; Palmoplantar keratoderma