Nail Patella Syndrome Genetics

Nail patella syndrome or NPS, is a genetic disorder passed down to children from their parents. It is usually present at birth and identified easily by a visual examination of the condition of the nails of the infant.

The nails may be missing altogether or may be misshaped. While the nails are not the only organ affected by NPS, they are the easiest to see and are often used for a preliminary diagnosis. Since associated risks of internal organs may remain asymptomatic for a long time, most doctors will not go looking for trouble unless they see this primary symptom prominently displayed.

Genetic transfer of nail patella syndrome

NPS is an autosomal dominant trait. All human traits are produced as a result of interaction of two genes. One of the genes comes from the mother, the second from the father. In order for a trait to be passed on both parents’ genes should support it.

Most genetic diseases tend to get passed on only when both parents have the defective gene. However, with an autosomal dominant trait, the diseased gene is strong enough to dominate the healthy gene from the other parent. That is why the disease is quite likely to be passed on to the child even if a single parent suffers from it.

In lay man’s terms this essentially means that if one of the parents has NPS, the child has a 50% likelihood of inheriting it as well. This inheritance pattern is not the only way to get the gene. There is no guarantee that, if the parents don’t have the disease the child will not have it either.

Apparently in cases where neither parent has NPS, the child may still develop the syndrome due to random mutations affecting the perpetuating gene. Conditions for the mutation of the gene are still being studied by genetic scientists.

Gene causing nail patella syndrome

The defective gene that causes NPS is called LMX1B and it is mapped to chromosome 9q34. Chromosomes are present in the nucleus of every cell in the human body. They carry the genetic characteristics of the individual. There are a total of 23 chromosomes in humans numbered from 1 to 23. The first 22 are common to both genders, while the 23rd pair is the X and Y chromosome for males and a double X chromosome for females.

Each chromosome has a short arm represented by “p” and a long arm represented by “q”. The chromosome arms are further divided into numbered bands. Here the gene on chromosome 9q34 refers to the gene on the long arm of the 9th chromosome and its 34th band. The LMX1B gene is in charge of regulating a protein which helps the unborn fetus in its growth and development.

The protein has the task of binding the DNA at certain points. The LMX1B gene is called a transcription factor as besides directing the production of the protein, it regulates the activity of other genes. The mutation of this gene is what causes the abnormal development of nails, kneecaps, elbows, and other skeletal defects in the embryo.

Diagnostic tests for nail patella syndrome

It is possible to use prenatal testing to find out if the fetus is likely to have the disorder. If one parent is suffering from the disorder they may wish to find out if the child will inherit it.

Ultrasound imaging tests of a special type can be used to create a real time image of the developing embryo to check for the syndrome. A visual examination of the nails of the child at birth can also be the basis of diagnosing NPS.

If the examining health care practitioner suspects the presence of NPS and it is not obvious through a physical examination of the nails, X-rays, computerized tomography (CT) scans, or magnetic resonance imaging (MRI) may be used to detect the bone based anomalies such as iliac horns, missing or misshaped patella, or any other dysplasia indicative of the presence of the disorder.

Suggested follow up tests

Should the diagnostic tests prove the presence of NPS, the individual should be monitored for a host of other features that could cause complications. The health of an individual with this disorder needs to be carefully monitored and each possible organ which may be affected should be tested.

Patients suffering from NPS should be encouraged to report any conditions that they are suffering from right away so that appropriate treatment can be carried out.

Eye tests could include checking for micro cornea, developing cataracts, Lester iris, and other possible issues. The individual should get a kidney tissue examination done so that the renal biopsy can rule out or identify the traces kidney disease.

Anemia and edema may also be symptomatic of kidney related disorders caused due to NPS. The spine should also be monitored for scoliosis or sideways curvature of the spinal column. The more care the individual takes, the faster any NPS associated symptoms can be caught and treated.

References

1. http://rarediseases.org/rare-diseases/nail-patella-syndrome/
2. http://www.nhs.uk/conditions/nail-patella-syndrome/Pages/Introduction.aspx
3. http://rarediseases.org/rare-diseases/nail-patella-syndrome/

Further Reading

• All Nail Patella Syndrome Content
• Nail Patella Syndrome Features
• How to Manage Nail Patella Syndrome