Overview of Pachyonychia Congenita
Pachyonychia congenita (PC) is a very rare genetic disorder that affects the skin and nails. The symptoms usually begin at birth or early in life, and the condition affects people of both sexes and all racial and ethnic groups.
PC is caused by mutations affecting keratins, proteins that provide structural support to cells, and it is classified into five types based on which keratin gene harbors the mutation. Symptoms vary from person to person and depend on the type, but thickened nails and calluses on the soles of the feet occur in almost all cases. The most debilitating symptom is painful calluses on the soles that make walking difficult. Some patients rely on a cane, crutches, or a wheelchair to help manage the pain of walking.
There is no specific treatment for PC, but there are ways to manage the symptoms, including the pain.
Who Gets Pachyonychia Congenita?
People who have pachyonychia congenita have a mutation in one of five keratin genes. Researchers have found more than 115 mutations in these genes that are linked to the disorder. In some cases, PC is inherited from a parent, while in others, there is no family history and the cause is a spontaneous mutation. The disorder is genetically dominant, which means that a single mutated gene copy is enough to cause the condition. PC is very rare. It affects people of both sexes and all racial and ethnic groups.
Types of Pachyonychia Congenita
There are five types of pachyonychia congenita, and they are classified based on the keratin gene that is altered. Thickened nails and painful calluses on the soles of the feet are typical of all forms of the disorder, but the presence of other features can depend on which keratin gene is affected, and possibly on the specific mutation.
Symptoms of Pachyonychia Congenita
The symptoms and severity of PC can vary widely, even among people with the same type or in the same family. Most symptoms typically appear within the first months or years of life.
The most common features of PC include:
- Painful calluses and blisters on the soles of the feet. In some cases, the calluses itch. Calluses and blisters may also form on the palms of the hands.
- Thickened nails. Not all nails are affected in every patient with PC, and some people do not have any thickened nails. But the vast majority of patients have some affected nails.
- Cysts of various types.
- Bumps around hairs at friction sites, such as the waist, hips, knees, and elbows. They are most common in children and lessen after the teenage years.
- White film on the tongue and inside the cheeks.
Less common features of PC include:
- Sores at the corners of the mouth.
- Teeth at or before birth.
- White film on the throat, resulting in a hoarse voice.
- Intense pain on first bite (“first bite syndrome”). The pain is near the jaw or ears and lasts 15–25 seconds when beginning to eat or swallow. This is more common in younger children and may cause feeding difficulties for some infants. It typically goes away during the teenage years.
Causes of Pachyonychia Congenita
Pachyonychia congenita is caused by mutations in genes that encode keratins, proteins that are the main structural components of skin, nails, and hair. The mutations prevent keratins from forming the strong network of filaments that normally gives skin cells strength and resilience. As a result, even normal activities like walking can cause cells to break down, ultimately leading to the painful blisters and calluses that are the most debilitating features of the disorder.