Pachyonychia congenita

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Pachyonychia congenita (PC) is an uncommon inherited skin disorder (Online Mendelian Inheritance in Man numbers 167200[4] & 167210[5]). The main clinical characteristic that gives the condition its name is abnormally thickened nails (pachy = thick; nychia = of the nails). There are, however, a number of other prominent features including focal palmoplantar keratoderma (painful, thickened skin on the soles and sometimes also the palms), oral and lingual leukokeratosis (white lesions in the lining of the mouth and tongue) and a variety of cysts, most often associated with hair follicles.

The disorder comes in two forms known as PC1 and PC2. In PC1, the keratoderma tends to be more painful and is often highly debilitating. In PC2, there is a tendency to develop more skin cysts following puberty. Some individuals with PC2 also have natal teeth (a few poorly developed teeth present at birth which are usually quickly shed).

The condition is caused by genetic mutations in one of four genes that encode keratin proteins specific to the epithelial tissues affected in the two forms of the disorder. PC1 is caused by mutations in keratin 6a (protein name K6a; gene name KRT6A) or keratin 16 (K16; KRT16). The PC2 form is due to mutations in the genes encoding keratin 6b (K6b; KRT6B) or keratin 17 (K17; KRT17). Three of the genes causing PC were identified in 1995[1][2] with the fourth gene following in 1998.[3]

PC follows an autosomal dominant pattern of inheritance, i.e. on average 50% of the offspring of an affected person will inherit the disorder, regardless of gender. Often, a solitary case exists in a family and these are due to occurrance of a new mutation (often referred to as a sporadic or spontaneous mutation).

A patient support group exists for helping individuals affected by PC, called "PC Project". They actively seek PC patients, offer help and support, organise meetings for patients and researchers, and sponsor research into developing new treatments for the condition, which is presently incurable. A wealth of information on all aspects of PC can be found on their website ([6]).

[edit] References

  1. ^ McLean WHI et al. (1995) Keratin 16 and keratin 17 mutations cause pachyonychia congenita. Nature Genetics 9:273-278. Abstract available here[1].
  2. ^ Bowden PE et al. (1995) Mutation of a type II keratin gene (K6a) in pachyonychia congenita. Nature Genetics 10:363-365. Abstract available here[2].
  3. ^ Smith FJD et al. (1998) A mutation in human keratin K6b produces a phenocopy of the K17 disorder pachyonychia congenita type 2. Human Molecular Genetics 7:1143-1148. Abstract available here[3].
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