Hypodontia and nail dysgenesis (HND), also known as Witkop tooth and nail syndrome or TNS, is a form of ectodermal dysplasia, which affects the ectoderm, the outer layer of the developing fetus. Because the ectodermal layer develops into many parts of an infant's body, including the nails and teeth, these parts may not develop normally.
HND was first described by a dermatologist named Witkop in 1965 when he observed patients with tooth and nail problems. Patients with HND may also have symptoms that affect the hair. Unlike in many forms of ectodermal dysplasia, however, the sweat glands do not appear to be affected. Symptoms of HND have been found to vary widely among patients.
People with HND may have absent, widely spaced, or cone-shaped teeth with narrow crowns. Fingernails and toenails may be poorly developed, abnormally small, ridged, spoon shaped, brittle, and slow to grow. Rarely, the nails separate from the nail beds and fall off. In people with HND, the toenails are generally more severely affected than the fingernails. Occasionally, sparse scalp hair is observed in HND.
HND is an inherited genetic disorder that is passed down from parents to children. It is caused by a mutation or defect in the MSX1 gene. This gene is known to be involved in tooth development. The disorder follows an autosomal dominant inheritance pattern, meaning only one copy of the defective gene is needed for the disease to appear.
HND is extremely rare with an estimated incidence between one in 1,000 and one in 10,000 people. HND affects males and females in equal numbers. Witkop suggested that the condition was more common among Dutch Mennonites in Canada than other populations.
While there is currently no known cure for HND, treatment focuses on reducing symptoms and managing or preventing complications.
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