Gorlin et al. (1976) suggested that 2 distinct syndromes are subsumed under the designation pachyonychia congenita. PC1, the Jadassohn-Lewandowski syndrome (167200), shows oral leukokeratosis. PC2, the form of Jackson and Lawler (1951-52), has natal teeth and epidermoid cysts ... Gorlin et al. (1976) suggested that 2 distinct syndromes are subsumed under the designation pachyonychia congenita. PC1, the Jadassohn-Lewandowski syndrome (167200), shows oral leukokeratosis. PC2, the form of Jackson and Lawler (1951-52), has natal teeth and epidermoid cysts (cylindromas), but no oral leukoplakia. Corneal dystrophy may be a feature exclusively of the Jackson-Lawler type. Both disorders are clearly autosomal dominant. Smith et al. (1998) stated that PC2, in contrast to PC1, has minimal oral involvement and milder keratoderma, and multiple steatocystomas (184500) is a major clinical feature (Smith et al., 1998). Steatocystoma, also known as eruptive vellus cyst, is a cystic hamartoma lined by sebaceous ductal epithelium. Jackson and Lawler (1951-52) reported 6 affected members of 3 generations. In 4 generations of a family, Vineyard and Scott (1961) observed steatocystoma associated with pachyonychia congenita. Hodes and Norins (1977) reported the same association. Soderqvist and Reed (1968) described the same association but thought that the cysts were epidermal cysts. They presented an interesting, illustrated newspaper clipping that described neonatal teeth in persons of 3 generations. The adult teeth were sound. Clementi et al. (1986) described a family in which 3 members in 2 generations had pachyonychia congenita, hyperkeratosis, and hyperhidrosis of the palms and soles, follicular keratosis, neonatal teeth, and epidermoid cysts. They pointed out that this is the rarer form of pachyonychia congenita. Armpit folliculitis was described in the 21-year-old proposita and in her 61-year-old mother. Cysts in the metacarpal and elbow regions were observed at puberty in the daughter. They were noted to adhere to the overlying skin on the elbows, dorsal surface of the proximal phalanges, and on the knees and pretibial regions. On the basis of a study of 13 patients with PC1 or PC2, Terrinoni et al. (2001) concluded that the presence of pilosebaceous cysts following puberty is the best indicator of PC2; prepubescent patients are more difficult to classify due to the lack of cysts. Natal teeth are indicative of PC2, although their absence does not preclude the PC2 diagnosis.
In affected members of a family segregating PC2, Smith et al. (1998) identified heterozygosity for a mutation in the KRT6B gene (148042.0001).
Terrinoni et al. (2001) studied 13 patients with PC1 or PC2 and found mutations ... In affected members of a family segregating PC2, Smith et al. (1998) identified heterozygosity for a mutation in the KRT6B gene (148042.0001). Terrinoni et al. (2001) studied 13 patients with PC1 or PC2 and found mutations in K6A (148041), K16 (148067), or K17 in all cases. They concluded that K6A or K16 mutations produce the PC1 phenotype, whereas K17 or K6B mutations cause PC2. In the kindred with PC2 studied by Munro et al. (1994), McLean et al. (1995) showed that a heterozygous asn92-to-asp mutation (148069.0001) in the helix initiation motif of keratin-17 cosegregated with the disease.