Overview of Pachyonychia Congenita
Pachyonychia congenita (PC) is a rare genetic disorder that primarily 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.
Symptoms of PC vary from person to person and depend on the type of PC that the individual has. There are five different types of PC, based on the keratin gene that is involved. Keratins are the main structural components of skin, nails, and hair. People with PC are most affected by severely painful calluses (hardened areas of skin) in the feet, which make walking difficult. Many individuals with PC 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 pain and other symptoms.
Who Gets Pachyonychia Congenita?
People who have pachyonychia congenita have a mutation (change) in one of five keratin genes. Researchers have found more than 125 different mutations in these five 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.
Types of Pachyonychia Congenita
There are five types of pachyonychia congenita, and each type is classified based on the keratin gene that is altered (changed). 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 depends on which keratin gene is affected, and 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:
- Thickened nails. Not all nails are affected in every person with the disorder, and some people do not have any thickened nails. But most people with PC have some affected nails.
- Painful calluses and blisters on the soles of the feet. Blisters are found under the calluses in people with PC. Calluses may also form on the palms of the hands.
- Cysts (sac-like pocket of tissue) of various types. In some forms of PC, cysts are the most painful and problematic feature.
- 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. This is not painful but is often misdiagnosed as thrush (a fungal infection) or as leukoplakia (thick, white patches) in young children.
- Deep itching under, around, or in the calluses can interfere with sleep and cause discomfort in the feet.
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 cry or voice. The condition can block the airway and become life-threatening, requiring immediate medical attention.
- Intense pain on first bite (“first bite syndrome”). The pain is near the jaw or ears and lasts 15 to 25 seconds when beginning to eat or swallow. This is more common in younger children, is often linked with ear problems, and may cause feeding difficulties for some infants. It typically lessens as children get older.
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 change the affected keratin proteins in ways that are still not fully understood. As a result, even normal activities like walking can cause cells to break down, ultimately leading to painful blisters and calluses that are the most debilitating features of the disorder.