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Nail-Patella syndrome is a rare genetic disorder characterized by abnormalities of bone, joints, fingernails and kidneys. It is commonly characterized by absent or under-developed kneecaps and thumbnails.

Less common medical findings include defects of the upper lip and the roof of the mouth. Skeletal abnormalities are also an important symptom of this condition and they may include poorly developed scapulae, sideways bent fingers, clubfoot, scoliosis, and unusual neck bones.
Experts have found an association between nail-patella syndrome and colon cancer. It is also proven that nail-patella syndrome is associated with open-angle glaucoma, which can sometimes lead to blindness. Patients may also have cataracts, drooping eyelids, or corneal problems. Symptoms vary from person to person even within a single family with multiple affected members.

NPS is also known as:

    * Fong Disease
    * Hereditary Onycho-Osteodysplasia
    * Iliac Horn Disease
    * Turner-Kieser syndrome

Incidence

The syndrome is estimated to occur in one in 50,000 newborns. The incidence of nephropathy in NPS is reported to be approximately 40% among patients with various degrees of dysfunction. Of these patients, 10% die of renal insufficiency. Both sexes are equally affected.

The Cause of Nail Patella Syndrome

Nail-patella syndrome has been recognized as an inherited disorder for over a hundred years. It is caused by mutations in a gene known as LIM Homeobox Transcription Factor 1-Beta (LMX1B), located on the long arm of chromosome 9. It has been proven that this gene codes for a protein that is important in embryonic limb development. Mutations in this gene have been detected in many unrelated people with nail-patella syndrome. When a parent has NPS, each of their children has a 50% chance to inherit the disease-causing mutation.

Symptoms of Nail-Patella syndrome

 NPS symptoms vary widely between patients, and some patients with this disorder do not display symptoms at all.

    * Fingernails

The most obvious sign associated with nail-patella syndrome are absent, poorly developed, or unusual fingernails. These symptoms are found in over 80% of patients with this disorder. The abnormalities may be found in one or more fingernails. This disease most commonly affects the fingernails of the thumbs and index fingers, which are often small and concave with pitting, ridges, splits, and discoloration. Patients have reported that their toenails are less often affected. 

    * Kneecaps

Kneecap abnormalities are the second most common sign associated with this disorder. One or both kneecaps may be missing or poorly formed. Even when present, they are likely to be dislocated. While patellae (kneecaps) normally have a nice and round shape, the knees of people with nail-patella syndrome may have a square appearance. Besides the kneecap, other support structures including bones, ligaments, and tendons may also be malformed. In some cases patients have problems with simple walking.

    * Hip bones

The hip bones of approximately 80% of patients with nail-patella syndrome have unusual bony projections, called posterior iliac horns. These spurs are internal and not obvious unless they are detected by x-ray. In most cases they cause no symptoms whatsoever.

    * Kidneys

Kidney disease is present in at least 30% of patients with nail-patella syndrome. This is an extremely important complication; kidney failure is the most dangerous consequence of NPS. The earliest sign of kidney affection is the presence of protein or blood in the urine. Kidney involvement is progressive, so early diagnosis and treatment of renal disease is important.

    * The skin

The skin on the hands is often wrinkled and loose, but sometimes smoothes over the distal joint. Some people with NPS also experience a lack of flexibility in the distal knuckle of the fingers.

    * Skeletal problems

There are several skeletal symptoms which may occur in people with this rare disease. Patients with nail-patella syndrome may not be able to fully straighten their arms at the elbow.

Patients may also show other related symptoms such as:

          o bent fingers
          o poorly developed shoulder blades
          o clubfoot
          o hip dislocation
          o unusual neck bones
          o scoliosis

    * Eye problems

Eye problems related to NPS vary from person to person. The syndrome is associated with open angle glaucoma, caused by fluid blocked into the front chamber of the eye, eventually causing increasing eye pressure. If untreated, this increased pressure may lead to permanent damage of the optic nerve and irreversible blindness.

Nail-patella syndrome has also been associated with:

          o abnormalities of the cornea
          o cataracts
          o astigmatism
          o multicolored irises
          o loss of peripheral vision
          o blind spots
          o difficulty in adjusting to a dark room
          o blurred vision
          o sore, reddened eyes
          o appearance of halos or rainbows around lights
          o severe headaches, nausea and eye pain

Diagnosis

    * Genetic testing: These last couple of years genetic testing for nail-patella syndrome has become available through research institutions working to further characterize the disorder. However, genetic testing still cannot predict which signs of the disease will develop, nor can it predict the severity of disease symptoms. That’s why it isn’t considered to be a first-choice diagnostic tool.

    * Physical evaluation: Diagnosis of this disease could also be made on simple visual medical clues such as the characteristic abnormalities of the fingernails and kneecaps.

    * X-Rays and biopsies: The best possible diagnostic tool is probably the x-ray. The diagnosis is confirmed by images of the affected bones and, when indicated, kidney biopsy. This is a reliable diagnostic method, since the bony pelvic spurs found in 80% of patients with nail-patella syndrome are not associated with any other known disease.

    * Prenatal diagnosis: A useful diagnostic tool could be third-trimester ultrasound. Prenatal diagnosis via genetic testing of cells obtained by chorionic villus could also be effective. Unfortunately, prenatal genetic testing for NPS is not yet widely available and it is being used only in specialized laboratories. Also, there have been some controversies surrounding the use of prenatal testing for such a variable disorder.

Treatment of Nail-Patella syndrome

Treatment is usually not necessary for cases of NPS. When required, it depends on each patient's specific symptoms.
Every severe kidney disease is treated with dialysis or a kidney transplant.
The treatment for glaucoma depends upon the nature and severity of each case; eye drops, pills, laser procedures, and surgical operations are used to prevent or slow further damage from occurring.
When walking becomes painful due to bone, tendon, ligament, or muscle defects, a wheelchair may be required. Of course, orthopedic surgery may be necessary for congenital foot deformity and hip dislocation. 

Prognosis

Survival among patients with nail-patella is decreased only if they experience renal complications. It is estimated that 8% of individuals with nail-patella syndrome who come to medical attention eventually die of kidney disease, although this isn’t a proven fact.