From OMIMPachyonychia congenita (PC) is an autosomal dominant genodermatosis with the main clinical features of hypertrophic nail dystrophy, painful and highly debilitating plantar keratoderma, oral leukokeratosis, and a variety of epidermal cysts. Although the condition had previously been subdivided clinically into Jadassohn-Lewandowsky PC type 1 and Jackson-Lawler PC type 2, patients with PC were later found to have a mixed constellation of both types, leading to a classification of PC based on genotype (summary by Sybert, 2010; Eliason et al., 2012; McLean et al., 2011).
Historical Classification of Pachyonychia Congenita
Gorlin et al. (1976) suggested that 2 distinct syndromes are subsumed under the designation pachyonychia congenita. PC type 1, the Jadassohn-Lewandowsky type, shows oral leukokeratosis. PC type 2, the Jackson-Lawler type, has natal teeth and epidermoid cysts (cylindromas), but no oral leukoplakia. Corneal dystrophy may be a feature exclusively of the Jackson-Lawler type.
Smith et al. (1998) stated that PC type 2, in contrast to PC type 1, has minimal oral involvement and milder keratoderma, and multiple steatocystomas (184500) is a major clinical feature. Steatocystoma, also known as eruptive vellus cyst, is a cystic hamartoma lined by sebaceous ductal epithelium.
On the basis of a study of 13 patients with PC type 1 or type 2, Terrinoni et al. (2001) concluded that the presence of pilosebaceous cysts following puberty is the best indicator of PC type 2; prepubescent patients are more difficult to classify due to the lack of cysts. Natal teeth are indicative of PC type 2, although their absence does not preclude the PC type 2 diagnosis.
Genetic Heterogeneity of Pachyonychia Congenita
See pachyonychia congenita-2 (PC2; 167210), caused by mutation in the KRT17 gene (148069) on chromosome 17; PC3 (615726), caused by mutation in the KRT6A gene (148041) on chromosome 2; and PC4 (615728), caused by mutation or in the KRT6B gene (148042) on chromosome 12.
See 260130 for a possible autosomal recessive form of pachyonychia congenita.
http://www.omim.org/entry/167200 From MedlinePlus GeneticsResearchers used to classigy pachyonychia congenita as either PC-1 or PC-2 based on the genetic cause and pattern of signs and symptoms. However, as more affected individuals were identified, it became clear that the signs and symptoms of the types overlapped considerably. Pachyonychia congenita is now classified into five types based on the gene that is altered.
Some affected individuals also develop widespread cysts called steatocystomas, which are filled with an oily substance called sebum that normally lubricates the skin and hair. Some babies with pachyonychia congenita have prenatal or natal teeth, which are teeth that are present at birth or in early infancy. Some babies and children with pachyonychia congenita have pain in one or both ears when beginning to eat or drink. Pachyonychia congenita can also affect the voice box (larynx), causing hoarseness or breathing problems.
Pachyonychia congenita can have several additional features. These features include thickened skin on the palms of the hands (palmar keratoderma), which can be painful; thick, white patches on the tongue and inside of the cheeks (oral leukokeratosis); bumps that develop around hair follicles (follicular keratoses) on the elbows, knees, and waistline; cysts in the armpits, groin, back, or scalp; and excessive sweating on the palms and soles (palmoplantar hyperhidrosis).
Most people with pachyonychia congenita also show some signs of hypertrophic nail dystrophy, which causes the fingernails and toenails to become thick and abnormally shaped. The number of affected nails varies.
Almost everyone with pachyonychia congenita develops very painful calluses on the soles of the feet. This condition is known as plantar keratoderma. Calluses usually begin to form on the feet in childhood when kids first start to walk. The calluses can make walking painful or impossible. In some affected individuals, blisters, bundles of blood vessels and nerves (neurovascular structures), or a deep itch may develop under or near the calluses, increasing pain and discomfort.
Pachyonychia congenita is a condition that primarily affects the skin and nails. The signs and symptoms of this condition usually become apparent within the first few years of life.
https://medlineplus.gov/genetics/condition/pachyonychia-congenita