Nail patella syndrome is a rare genetic condition that can cause problems with the nails, bones, kidneys and eyes. It's thought to affect at least one in 50,000 people.
Symptoms vary, but almost everyone with the condition will have abnormal nails and many also have problems with their elbows, knees and pelvis. However, most people are able to lead relatively normal lives.
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. Some of the problems will be obvious from birth, but others may not become apparent until later on.
Nearly all people with nail patella syndrome will have abnormal or missing 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 nails are less severely affected from the index finger towards the little finger. Toenails are generally less affected than fingernails.
Other areas of the body that can be affected include the bones and joints, kidneys and eyes.
Common features include:
knees – missing 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 may be visible on X-rays, but 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) and this can be accompanied by blood in the urine; in some cases, this can progress to kidney disease, with high blood pressure and kidney failure
nerves – numbness and a tingling or burning sensation in the hands and feet
circulation – poor blood circulation in the hands and feet, causing them to feel cold, even in warm weather
digestive system – about one in three people have constipation orirritable bowel syndrome (IBS)
body size – difficulty putting on weight, particularly muscle, despite eating and exercising well, with little muscle mass in the upper arms and upper legs
thin bones (osteoporosis) – notably in the hips
hairline – the hairline may be high, particularly at the temples
It has also been suggested that people with nail patella syndrome may be more likely to have attention deficit hyperactivity disorder (ADHD) ordepression, although more research is needed to confirm this.
What causes nail patella syndrome?
Most people with nail patella syndrome will have inherited a defective version of a gene called LMX1B from one of their parents. This gene is important in the development of a baby's limbs, nails, kidneys and eyes.
Only one of the two copies of the gene needs to be faulty for a person to be affected (dominant inheritance). This means a child of someone with nail patella syndrome has a 50% chance of inheriting the condition.
However, there is not always a family history of nail patella syndrome. In some cases, the LMX1B gene will have mutated (altered) spontaneously.
The diagnosis of nail patella syndrome is usually based on the symptoms you or your child has. However, when the diagnosis is not clear, a genetic blood test can be used to confirm the diagnosis by finding out whether a person is carrying a mutated LMX1B gene. A mutation in this gene can be identified in 95% of people with nail patella syndrome.
Genetic testing can also be carried out during pregnancy to find out if a child will be born with nail patella syndrome, although this cannot predict how severe the condition will be.
Another option for couples at risk of having a child with nail patella syndrome is a technique called pre-implantation genetic diagnosis (PGD). This involves testing embryos that have been fertilised using in vitro fertilisation (IVF), and only implanting embryos that have not inherited nail patella syndrome into the womb.
Before genetic testing or PGD, genetic counselling will be offered. This 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.
Managing nail patella syndrome
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. However, long-term use of non-steroidal anti-inflammatory drug (NSAID)painkillers should be avoided, because these can affect the kidneys.
Some people may need corrective surgery for problems with the bones and joints.
Annual urine tests to look for kidney problems should begin at birth. If problems develop, these may need to be controlled with medication ordialysis (where a machine is used to replicate many of the kidney’s functions). People with severe kidney disease may need to have akidney transplant.
Women with high blood pressure caused by kidney problems will need to be carefully monitored if they become pregnant, as pregnancy can make high blood pressure worse.
Screening for glaucoma should start in the teenage years and be repeated at least every two years. Treatment for glaucoma may involve using eye drops or having a procedure to reduce the pressure inside the eye.Assessment of bone density is recommended for young adults to check for osteoporosis.