This is a rare genetic disorder characterized by the abnormalities of the nails, elbows, knees and the pelvis. The symptoms of this condition are usually evident at the birth of the infant or during early childhood. The symptoms and the features of the disease vary greatly among the affected cases but commonly includes the improper development of the fingernails and toenails, underdevelopment of the kneecaps, limited movement of the elbow and abnormal projection of the bone on both the sides of the hipbone.
Causes
Nail-patella develops because of the mutation in the gene identified as LMX1B which produces a protein that binds to the DNA and LMX1B protein is also known as a transcription factor. This protein is essential during the embryonic development of various parts of the body such as the limbs, kidneys and the eyes. The genetic mutation results in the production of nonfunctional protein causing the symptoms associated with this condition. Nail-patella syndrome is inherited in an autosomal dominant pattern meaning a single copy of the defective gene can cause the disorder. In some cases, it can be the result of a new genetic mutation that occurs among people with no history of the disease in their family.
Symptoms
In most cases, the nail changes are the common feature of the condition which is evident at the birth of the infant or can occur in early infancy. The nails can be abnormally short, split, thickened or discolored. In some cases, the toenails may also be involved. The abnormalities of the bones include underdeveloped or absent kneecaps, limited movements of the knees, progressive degeneration and pain of the knees. They can also present abnormalities of the elbow bones, bone projections from both the sides of the hipbone, underdevelopment of the shoulder blade and sideway curvature of the spine. Some of the cases can present glaucoma which is the increased pressure of the eyes that can cause blurred vision, headaches, narrowing of visual fields and eventually blindness. In around 50% of the cases, the kidney problems can also occur which can include nephrotic kidney disease and glomerular kidney disease.
Diagnosis
The disorder may be suspected based on the identification of characteristic features at the birth of the infant or in early childhood. Various specialized tests such as x-rays, CT scan and MRI scans may be required to determine the extent of bone abnormalities. Genetic testing can help confirm the diagnosis by identifying the mutation responsible for causing the condition.
Treatment
There is no cure for the disease and the treatment is focused on the management of the symptoms. The bone abnormalities can include surgical intervention for the replacement of knee caps and correction of bone abnormalities. The curvature of the spine can be treated with exercises, physical therapy, braces or corrective surgery. In the case of problems with the eye, the treatment options can include corrective glasses, contact lenses or surgery to improve vision. Also, the blood pressure and the kidney function should be regularly monitored for complications which need prompt treatment. Genetic counseling may be beneficial for some of the affected cases and their family members.
References
https://ghr.nlm.nih.gov/condition/nail-patella-syndrome
https://rarediseases.org/rare-diseases/nail-patella-syndrome/
http://www.nhs.uk/Conditions/nail-patella-syndrome/Pages/Introduction.aspx