Focal palmoplantar keratoderma

Focal palmoplantar keratoderma is a skin condition characterized by the development of painful blisters and calluses on the soles of the feet and, less commonly, on the palms of the hands. The skin abnormalities usually begin in childhood, and they primarily affect areas that experience trauma or friction. Severe blisters and calluses on the feet can cause pain and difficulty walking.

Some people with focal palmoplantar keratoderma also have very mild abnormalities of the fingernails and toenails.

Focal palmoplantar keratoderma appears to be a rare condition, although its prevalence is unknown.

Focal palmoplantar keratoderma can result from mutations in the KRT6C gene or the KRT16 gene. These genes provide instructions for making proteins called keratin 6c and keratin 16. Keratins are tough, fibrous proteins that work together to provide strength and resilience to the tissues that make up the skin, hair, and nails.

Mutations in the KRT6C or KRT16 gene alter the structure of keratin 6c or keratin 16, preventing these proteins from interacting with other keratins to form strong, stable networks within cells. Without this network, skin cells become fragile and are easily damaged, making the skin less resistant to friction and minor trauma. The soles of the feet experience a significant amount of friction compared with many other parts of the body and must bear the body's weight, which may help explain why blisters and calluses primarily occur in this area in people with focal palmoplantar keratoderma.

Focal palmoplantar keratoderma is a major feature of a related skin disorder called pachyonychia congenita, which also results from mutations in keratin genes. In addition to blisters and calluses on the feet and hands, pachyonychia congenita is associated with severe nail abnormalities and skin problems affecting other parts of the body. Many researchers believe that focal palmoplantar keratoderma without these additional features represents a mild form of pachyonychia congenita.

Some people with focal palmoplantar keratoderma do not have an identified mutation in the KRT6C or KRT16 gene. The cause of the condition in these individuals is unknown.

Read more about the KRT6C and KRT16 genes.

Read more about pachyonychia congenita.

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from an affected parent. Other affected individuals have no family history of the condition.