Pincer nail deformity as the main manifestation of Clouston syndrome.

Abstract

Funding sources: National Taiwan University Hospital Fund. Conflicts of interest: none declared. Dear Editor, Pincer nail deformity is characterized by an increase in the transverse curvature along the longitudinal axis of the nail.1 Acquired pincer nails are not symmetrical. The most common causes are onychomycosis, psoriasis, tumours of the nail apparatus, and poorly fitting shoes.2 3 Pincer nail deformity may be associated with systemic diseases, such as renal failure.4 Hereditary pincer nail deformity is rare and only a few cases have been reported.5 Clouston syndrome is an autosomal dominant hidrotic ectodermal dysplasia initially suspected to be caused by a defect in the keratin proteins.6 It is characterized by alopecia, palmoplantar hyperkeratosis and nail dystrophy. In 1996, the GJB6 gene, encoding connexin‐30, was determined to be mutated in these patients.7 The c.31G>A (p.G11R) mutation was first identified in two unrelated French families, and other disease‐causing mutations in the gene were also identified.7 8 The spectrum of clinical manifestations of Clouston syndrome was later extended to include pachyonychia congenita,9 a group of ectodermal dysplasias with the most obvious phenotypic characteristics of subungual hyperkeratosis and palmoplantar keratoderma. Pachyonychia congenita is associated with mutations in keratins 6a, 6b, 16 and 17.10 11 Several families with nail abnormalities had previously been diagnosed as having pachyonychia congenita; subsequently GJB6 p.G11R and p.A88V mutations were identified, and those patients actually exhibited Clouston syndrome.9