Nail patella syndrome: Causes, symptoms, treatment, inheritance

Nail patella syndrome (NPS) is a rare genetic disorder. The symptoms vary depending on which areas of the body it affects. It commonly affects the nails, knees, elbows, and hips but can also affect the kidneys, the eyes, and other areas.

Treatments will depend on the location and severity of the symptoms. The condition often requires lifelong maintenance and monitoring.

This article reviews what nail patella syndrome is, the symptoms, the causes, and more.

NPS, formerly called Fong's disease, is a rare genetic condition that appears at birth or in early infancy.

The most common symptom is the appearance of underdeveloped or missing toenails or fingernails. However, NPS can also affect a person's:

Additionally, NPS can cause fluid pressure to build up inside the eyes — a condition called glaucoma. Without treatment, chronic elevated pressure inside the eyes can lead to vision changes and, eventually, permanent loss of vision.

According to the National Organization for Rare Disorders (NORD), about 30–50% of people with this condition develop issues with their kidneys during childhood or adulthood, and about 5% may experience kidney failure.

The condition affects fewer than 50,000 people in the United States.

Symptoms of NPS can vary from person to person.

Nail changes are the most common symptom, affecting 98% of people with the condition. NPS most often affects the thumbnails but can mildly affect the other fingernails.

NPS does not always affect the toenails, but when it does, it may be apparent in the little toenail.

The nails may be:

Additionally, the pale, half-moon-shaped area at the base of the nail may be triangular.

NPS can affect the knees as well. The kneecaps may be small, underdeveloped, misshaped, or absent. This can cause a person to experience:

It can also cause one or both knees to bend outward.

If the condition affects the elbows, the parts of the bone that meet at the elbow may be small and underdeveloped. A person may also develop webbing of the skin at the bend of the elbow.

As a result, a person may not be able to fully extend or rotate their arm. Partial dislocation of the elbow can also occur.

Most people with NPS develop bilateral iliac horns, which are projections of bone on the hip bones.

Other possible symptoms include:

NPS is an autosomal dominant genetic condition.

People inherit traits and genetic conditions by receiving two copies of each gene — one copy from each biological parent.

According to NORD, a dominant genetic disorder occurs if a person receives just one affected copy of a gene. This means a person has a 50% chance of developing the disorder if one of their parents has an affected gene.

However, about 10% of all new NPS cases occur as a spontaneous mutation when neither parent has the condition.

Currently, the only known cause of NPS is a change, or mutation, in the LMX1B gene. Mutations in this gene cause changes and irregularities in the skeleton.

There is no correlation between the specific mutation and the range and severity of the condition.

Diagnosis can occur at birth, in early childhood, or later in life.

To diagnose the condition, a doctor will need to:

Imaging technologies such as X-rays and CT scans can help a doctor identify bone and joint irregularities.

Genetic testing for changes to the LMX1B gene can help confirm the diagnosis.

NPS may take a long time for doctors to diagnose. Delays in diagnosis can occur for the following reasons:

Treatment will depend on a person's symptoms and typically involves providing supportive care.

In many cases, treatment will involve coordination among several specialists and other healthcare professionals. Treatment teams for the condition can vary but may include:

If a person or their parent or guardian suspects they may have nail patella syndrome, speaking with a primary care doctor may be a good first step. The doctor may be able to help determine whether someone has the condition and help build a team of specialists to provide treatments.

Treatments may include:

Nail patella syndrome is a rare condition affecting fewer than 50,000 people in the United States.

In about 10% of those people, the condition occurs as a spontaneous mutation of the LMX1B gene. About 90% of cases occur as a result of a person passing the condition down to their child.

A person with the condition has a 50% chance of passing down the dominant gene.

The percentage does not change in subsequent births, which means each child has a 50% chance of developing the condition.

A person with a diagnosis of NPS may wish to seek genetic counseling before having children. Speaking with a doctor may help those who want to have children plan for the potential of passing the condition to a child.

A person who has received a diagnosis of NPS will likely need yearly screenings to check for the development of complications such as reduced kidney function, problems with the eyes, and high blood pressure.

Some people will need ongoing aid and support such as maintenance medication or assistive devices for movement. A person may also need physical or occupational therapy.

With monitoring and treatment, a person with NPS can generally maintain a high quality of life. However, the condition's potential effects on the kidneys may influence a person's overall outcome.

NPS is a rare genetic disorder that can affect several areas of the body but most often affects the nails.

The most common symptom is the appearance of underdeveloped or missing toenails or fingernails. However, NPS can also affect the elbows, kneecaps, hip bones, and eyes.

It is a lifelong condition. However, with monitoring and treatment to manage the symptoms, a person can generally maintain a high quality of life.