Nail-Patella Syndrome is a rare genetic disorder that often results in deformities of the kneecaps, thumb and finger nails, elbows, pelvis, and ankles. The syndrome is named for the two most common manifestations: deficiency of the nails and the patellas (kneecaps). However, Nail-Patella Syndrome affects the entire body. Joint contractures are a common feature of this syndrome, and many affected individuals develop arthritis of their joints.
Abnormalities of the nails is the most common feature in individuals with Nail-Patella Syndrome. The thumbnails are more severely affected, and deformities of the fingernails occur more often than deformities of the toenails. The nails of affected individuals are poorly developed, with only a small piece of nail present or sometimes with no nail at all. The nails may also be discolored or triangular shaped (rather than the normal crescent shape).
The second most common feature of Nail-Patella Syndrome is deformity of the kneecaps (patella). The kneecaps are smaller than normal or absent in some cases. They are also typically irregularly-shaped, and dislocation of the patella occurs frequently. Affected individuals often have similar deficiencies of the elbow and hip joints. Individuals with elbow deformities usually have difficulty extending their arms straight and rotating their forearms. In the hip, affected individuals may outgrowths in the iliac bone.
Other areas of the body may also be affected in Nail-Patella Syndrome. Glaucoma of the eyes and kidney diseases, such as proteinuria and nephritis, may also be present.
Nail-Patella Syndrome is quite rare, affecting 1 in 50,000 individuals. The syndrome is linked to mutations in the LMX1B gene, which codes for a protein that binds to the DNA and regulates other genes. This protein is thought to be important to the development of limbs, the kidneys, and the eyes in early development. Nail-Patella Syndrome is inherited in an autosomal dominant fashion, meaning only a single copy of the gene is required to express symptoms.