Nail patella syndrome is an uncommon genetic condition that causes problems with the nails, bones, kidneys and eyes.
It is thought to affect about one in 50,000 people, with some people more severely affected than others.
Symptoms vary, but almost all people with nail patella syndrome will have abnormal nails and also often have problems with their elbows, knees and pelvis. However, most are able to lead a relatively normal life.
What are the typical features?
The main signs and symptoms of nail patella syndrome are listed below.
Someone with the condition may not have all these symptoms and some symptoms may be more severe than others.
Most people with nail patella syndrome will have abnormal or absent nails, which is usually apparent at birth.
The base of each nail is often triangular, rather than a curved crescent shape, and the nails themselves may be underdeveloped, discoloured, split, ridged or pitted.
Thumbnails are the most severely affected, and the severity tends to decrease towards the little finger. Toenails are generally not as severely affected as fingernails.
Many people with nail patella syndrome also have problems with other areas of the body, including the bones and joints, kidneys and eyes.
Common features are:
- knees – absent kneecaps (patellas) or kneecaps that are small, irregularly shaped and easily dislocated (may feel unstable or painful)
- arms and elbows – not able to fully extend the arms or turn the palms up while keeping elbows straight, and elbows may angle outwards
- pelvis – bony growths (iliac horns) on the pelvic bone apparent on X-ray, which don't usually cause problems
- eyes – increased pressure within the eyes (glaucoma) at an early age
- kidneys – there may be protein in the urine (an early sign of kidney problems), which could progress to kidney disease and kidney failure
- body size – difficulty putting on weight, particularly muscle, despite eating and exercising well, and a decrease in muscle mass in the upper arms and upper legs
- hairline – the hairline may be high, particularly at the temples
What is the cause?
Most people with nail patella syndrome will have inherited a defective gene, called LMX1B, from one of their parents. Only one copy of the altered gene is needed to develop the condition (dominant inheritance).
A child of someone with nail patella syndrome has a 50% chance of inheriting the condition.
Read about how genetic conditions are inherited.
However, there is not always a family history of nail patella syndrome. In some cases, the LMX1B gene will have mutated (altered) spontaneously. It's not understood why this happens.
The LMX1B gene
Genes are units of DNA that provide instructions for making the proteins needed by your body.
The LMX1B gene codes for a protein that regulates the activity of other genes. It's particularly important during the early development of a baby's limbs, kidneys and eyes while in the womb.
The mutated LMX1B gene leads to the production of an abnormal protein that doesn't work properly.
The diagnosis of nail patella syndrome is usually made based on clinical features.
However, when the diagnosis is not clear, genetic testing can be used to find out whether a person is carrying the mutated LMX1B gene that causes nail patella syndrome.
This usually involves having a sample of blood taken. The sample will include cells that contain the person's DNA.
Before genetic testing is done, genetic counselling will be offered. This counselling service is provided by healthcare professionals specially trained in the science of human genetics (a genetic counsellor or a clinical geneticist) and is available at regional genetics centres across the country.
The counsellor will discuss the risks, benefits and limitations of genetic testing. They will also explain how the information found as a result of genetic testing could have implications for both you and your family.
Learn about pre-implantation genetic diagnosis, a service that's available to couples who are at risk of having a child with nail patella syndrome.
What is the outlook?
There is no cure for nail patella syndrome, but treatments are available to manage the symptoms.
For example, knees that are easily dislocated and painful can be helped with painkillers, physiotherapy, splinting and bracing.
Some people may need corrective surgery for problems with the bones and joints. The consultant or surgeon will explain the procedure in detail, as well as the risks and benefits.
Read about having an operation.
Kidney problems may need to be controlled with medication. People with severe kidney disease may need to have a kidney transplant.
Urine tests for kidney disease and blood pressure management should begin at birth and be repeated yearly. Screening for glaucoma should begin in adolescence and be repeated yearly.
Learn more about testing for glaucoma.
People with nail patella syndrome should be cautious about the long-term use of painkillers called NSAIDS (non-steroidal anti-inflammatory drugs), as these may make any kidney problems worse.