Pachyonychia congenita is a rare genodermatosis due to mutations in one of four keratin genes. It is characterized by dystrophic, thickened nails and painful palmoplantar keratoderma. Müller made one of the first documented observations of pachyonychia congenita in 1904.
The next reports were published in 1905 by Wilson
and in 1906 by Jadassohn and Lewandowsky.
Based on available case reports and small series, the disorder has historically been divided into 2 main subtypes. Pachyonychia congenita type 1, or the Jadassohn-Lewandowsky type (Mendelian Inheritance in Man (MIM entry 167200), was attributed to mutations in genes encoding keratin 6A (KRT6A) or keratin 16 (KRT16) and constituted the most common form of the disorder.
Pachyonychia congenita type 2, or the Jackson-Lawler type (MIM entry 167210), was attributed to mutations in keratin 6B (KRT6B) or keratin 17 (KRT17) and could be distinguished from type 1 by the development of natal teeth, widespread steatocystomas, and occasionally pili torti.
Recent large phenotype-genotype studies of patients from the International Pachyonychia Congenita Research Registry (IPCRR)
have provided a clearer picture of the disease and reveal a spectrum of overlapping clinical features that can be correlated genotypically to the specific mutations in patients with pachyonychia congenita.