A nonsense mutation in MSX1 causes Witkop syndrome.

Witkop syndrome, also known as tooth and nail syndrome (TNS), is a rare autosomal dominant disorder. Affected individuals have nail dysplasia and several congenitally missing teeth. To identify the gene responsible for TNS, we used candidate-gene linkage analysis in a three-generation family affected by the disorder. We found linkage between TNS and polymorphic markers surrounding the MSX1 locus. Direct sequencing and restriction-enzyme analysis revealed that a heterozygous stop mutation in the homeodomain of MSX1 cosegregated with the phenotype. In addition, histological analysis of Msx1-knockout mice, combined with a finding of Msx1 expression in mesenchyme of developing nail beds, revealed that not only was tooth development disrupted in these mice, but nail development was affected as well. Nail plates in Msx1-null mice were defective and were thinner than those of their wild-type littermates. The resemblance between the tooth and nail phenotype in the human family and that of Msx1-knockout mice strongly supports the conclusions that a nonsense mutation in MSX1 causes TNS and that Msx1 is critical for both tooth and nail development.

Features of oligodontia in three generations.

Congenitally missing teeth of three generations of a family and the spousal influence on the oligodontia of the third generation is investigated. For clarification, a review of commonly used terms is included in the paper. Although there are a number of factors affecting the failure to develop permanent tooth buds, most researchers believe that an autosomal dominant trait is responsible for the oligodontia in this family. Many syndromes are associated with oligodontia, but none seem to be prevalent in the direct descendants of the first generation. A member of the second generation married a person with Witkop's (tooth-and-nail) syndrome. Subsequently, their child exhibits the same manifestations. A feature noted in this three generation pedigree is missing permanent first molars. This is considered rare, especially when few abnormal ectodermal findings are reported. Additional findings include an increased number of missing teeth, decreased tooth size and a prominent maxillary labial frenum. The dental treatment for patients affected will likely involve a multidisciplinary approach. The treatment is particularly important since the lack of a full complement of teeth impacts the emotional and physical well-being of the individual. Children who are missing permanent teeth should be screened for other ectodermal abnormalities to rule out syndromes associated with congenitally missing teeth. Oligodontia is predicted to affect fifty percent of the fourth generation. It may vary in penetrance and expression.