Nail Patella Syndrome
Description, Causes and Risk Factors:
Alternative Names: Fong's disease, hereditary onycho-osteodysplasia [HOOD] or Turner-Kieser Syndrome.
Nail patella syndrome is a genetic condition which affects the nails, knees, elbows and can cause iliac horns (bony protrusions on the pelvis bones). There are, however, many other features that may be seen in this condition and other body systems such as the kidneys and eyes may be affected. In the skeletal system, tendons, ligaments and muscles can be affected as well as bones. The severity of the features of NPS and how often each feature occurs, varies between one person with NPS and another, even within the same family. A person with NPS does not have to have all of the features of the condition.
NPS is inherited in an autosomal dominant manner, that is, the risk of transmission is 50% per pregnancy. Approximately 20% of cases are sporadic, being the result of a new mutation (gene change).
The condition is found in approximately 1 in 50,000 of the population and occurs in all ethnic groups.
It has recently been shown that this disorder is caused by putative loss-of-function mutations in a transcription factor (LMXIB, which is located on chromosome number 9) belonging to LIM-homeodomain family, members of which are known to be important for pattern formation during development. However, there is no clear cut evidence. Although there was a remarkable high incidence of renal disease in patient with NPS, in most cases, the nephropathy manifest only by chronic benign proteinuria. It is unknown which factors are responsible for progression to renal insufficiency. In addition, evidence of a correlation between other characteristics of the NPS phenotype and specific mutation has not been found.
Researchers have found a strong evidence of link between glaucoma and NPS. The gene which mutates to cause NPS is located on a portion of chromosome 9 called 9q34. Studies have provided direct evidence that the glaucoma related genetic material is located at that same chromosomal site.
Common symptoms of the condition include abnormal kneecaps and thumbnails. The nails are usually missing or very short and can be discolored and easily split. Bones and joints are affected and the knees are often unstable.
A person may experience a limited range of motion in the elbows. Vision complications are another main characteristic of the disease and include loss of peripheral vision, red eyes, sore eyes, blurry vision, blind spots, headaches and difficulty adjusting in a dark room.
Nail changes are seen in 98% of patients with NPS but they may be subtle. Nails may be missing, small or abnormal, ridged, pitted, discolored, separated into two halves by a ridge of skin, thin or less often, thickened. Nail changes may be noticeable at birth and are most often on both hands and are usually symmetrical.
The thumbnails are the most severely affected nail, and the severity tends to decrease towards the little finger. Each individual thumbnail is usually more severely affected on the side next to the index finger. The only nail changes present may be triangular lunules, a characteristic feature of NPS, which means that the half moons seen at the base of the nail are pointed rather than rounded.
The toenails are usually less severely and less frequently involved than the fingernails.
Symptoms associated with knee abnormalities in NPS included pain, giving way, a feeling of instability, locking, clicking, patella dislocation and the inability to straighten the knee joint. Other occasional knee problems may include, quadriceps muscle wasting, genu recurvatum (knees bent backwards), genu valgum (knock knees), genu varum (bowlegs), different leg lengths, rotational deformities of the legs (twisted legs), Osgood-Schlatter's disease, osteochondritis dissecans, and absence or abnormality of the anterior cruciate ligaments. In some patients who have had knee operations for NPS the anatomy of the joint has been found to be abnormal, including abnormal muscle attachments.
There may be difficulty straightening the elbow, and one elbow may be more severely affected than the other elbow. Elbow contractures tend to stay the same over time. There may also be difficulties turning the hand over so the palm face upwards.
Renal involvement may result in proteinuria and recurrent UTI (urinary tract infections). Cutaneous manifestations are nail changes that involve mainly the thumb and progressively decrease in severity in the second to fifth fingers. Patient often complains of palmoplantar hyperhidrosis. Other nail abnormalities in patients with NPS are like splitting, longitudinal ridging, koilonychias, etc.
Diagnosis of this disease is most often made on visual medical symptoms such as the characteristic abnormalities of the fingernails and kneecaps. Diagnosis is confirmed by x-ray images of the affected bones and, when indicated, kidney biopsy. The bony pelvic spurs found in children with nail-patella syndrome are not associated with any other disease.
Genetic testing for nail-patella syndrome is usually available only at research institutions that are working to further characterize this disorder. However, genetic testing cannot predict which signs of the disease will develop nor predict the severity of disease symptoms.
During a pregnancy, it may be possible to tell whether a baby has inherited the NPS gene alteration by testing the pregnancy (prenatal diagnosis). However, it is not possible to predict how severely the baby would be affected. Prenatal testing via chorionic villus sampling (CVS) can be done at approximately 10 weeks of pregnancy. Ultrasound scans during a pregnancy may detect major problems with the limbs eg club foot, but most of the features of NPS would not be possible to detect on an antenatal ultrasound scan.
Treatment for children affected by nail-patella syndrome depends on the child's specific symptoms.
A wheelchair may be required if walking becomes painful due to bone, tendon, ligament, or muscle defects. Orthopedic surgery may be necessary for congenital clubfoot deformity. Manipulation or surgery may be required to correct hip dislocation. Cataracts are also surgically treated. Medical treatment at early signs of glaucoma prevents progression of the disease to blindness.
Controlling blood pressure may slow the rate of deterioration of kidney function. Severe kidney disease can be treated with dialysis or a kidney transplant. Children receiving kidney transplants do not develop nail-patella-type renal complications in their new kidney.
Because many possible manifestations of nail-patella syndrome exist, parents are advised to obtain extra medical care for their child with nail-patella syndrome, including regular urinalysis to monitor blood and protein levels to detect kidney disease as well as eye exams to detect glaucoma. Children with nail-patella syndrome should be periodically screened for scoliosis and lordosis
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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