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Nail-Patella Syndrome

Nail-Patella syndrome (NPS) is a rare genetic disorder that causes abnormalities of bone, joints, fingernails and kidneys. NPS is commonly characterized by absent or under-developed kneecaps and thumbnails. It is estimated to occur in one in 50,000 newborns.

Information about Nail-Patella Syndrome

Nail-patella syndrome (NPS) is a rare genetic disorder that is usually apparent at birth or during early childhood. Although the symptoms and physical characteristics associated with NPS may vary, characteristic abnormalities tend to include improper development (dysplasia) of the fingernails and toenails; absence (aplasia) and/or underdevelopment (hypoplasia) of the knee caps (patellae); underdevelopment of certain bones and/or webbing of skin at the bend of the elbow(s); and/or abnormal projections of bone from the upper (superior) portion of both sides of the hipbone (bilateral iliac horns).
In addition, some individuals within certain families (kindreds) may have abnormally increased fluid pressure of the eyes (glaucoma). The condition results due to progressive blockage of the outflow of fluid (aqueous humor) from the front chamber of the eyes (open-angle glaucoma). Without appropriate treatment, the gradual increase in fluid pressure may cause increased narrowing of visual fields and eventual blindness. Other eye (ocular) abnormalities may also be associated with NPS. For example, in some affected individuals, the inner margin (pupillary margin) of the colored portion of the eyes (irides) may appear abnormally dark (hyperpigmentation) and "cloverleaf shaped" (Lester iris).

Approximately 30 to 40 percent of individuals with NPS may also develop abnormalities in kidney function (nephropathy) that may be apparent during childhood or later in life. Nail-patella Syndrome is inherited as an autosomal dominant trait.

 

Causes of Nail-Patella Syndrome

Nail-patella syndrome is a rare genetic disease. The genetic mutation is an autosomal dominant mutation. This means that possession of only one copy of the defective gene is enough to cause disease. The defect has been mapped to chromosome 9 and may be related to the gene that codes for type 5 collagen. Some patients with this disease show no symptoms and are discovered to have the disease only when genetic studies trace family histories.

The fingernails of these patients are usually poorly developed or missing. The index fingers and thumb are most commonly affected by this disease. Fingernails that are present may be small and concave and have pitting, ridges, splits, and discoloration. Effects are rarely seen on the toes. Either or both kneecaps may be missing. Abnormally formed kneecaps can take a variety of shapes. Since the kneecap stabilizes the knee, patients may have difficulty walking. The iliac crest of the hip bone usually has a pronounced flaring called iliac horns. Kidney disease may be present. Biopsy shows lesions that resemble those of inflammation of the clusters of capillaries in the kidneys (glomerulonephritis), but without any infection present. Kidney failure occurs in about 30% of nail-patella patients who have kidney involvement. Most patients have excrete protein and blood cells in their urine (chronic, benign proteinuria and hematuria.)

Symptoms of Nail-Patella Syndrome

The phenotype is characterized by multiple osseous abnormalities, primarily affecting the elbows and knees and nail dysplasia. About 50% of patients have clinically evident nephropathy. The disease usually manifests clinically as asymptomatic hematuria and proteinuria, occasionally in the nephrotic range, but it may be silent. (Harrison's Principles of Internal Medicine-15th Edition-McGraw-Hill)

 
 
 
 
 
   

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05/27/2011

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