The TBX1 gene provides instructions for making a protein called T-box 1. Genes in the T-box family play important roles in the formation of tissues and organs during embryonic development. To carry out these roles, proteins produced from these genes bind to specific areas of DNA. The proteins attach to critical regions near genes and help control the activity of those genes. T-box proteins are called transcription factors on the basis of this action.
The T-box 1 protein appears to be necessary for the normal development of muscles and bones of the face and neck, large arteries that carry blood out of the heart, structures in the ear, and glands such as the thymus and parathyroid. Although the T-box 1 protein acts as a transcription factor, researchers have not determined which genes are regulated by this protein.
Most cases of 22q11.2 deletion syndrome are caused by a deletion of a small piece of chromosome 22. This region of the chromosome contains 30 to 40 genes, including the TBX1 gene. In a small number of affected individuals without a chromosome 22 deletion, mutations in the TBX1 gene are thought to be responsible for the characteristic signs and symptoms of the syndrome. The identified mutations include changes in single DNA building blocks (base pairs) in the TBX1 gene and deletions of a small amount of genetic material from the gene. Some of these mutations reduce the amount of T-box 1 protein that is produced in cells, while other mutations alter the protein's function. These genetic changes likely affect the ability of the T-box 1 protein to bind to DNA and regulate the activity of other genes.
Researchers believe that changes in the TBX1 gene, due to either a mutation in the gene or a deletion of part of chromosome 22, are responsible for many of the features of 22q11.2 deletion syndrome. Specifically, a reduction in the amount of T-box 1 or changes in the protein's normal function are associated with heart defects, an opening in the roof of the mouth (a cleft palate), distinctive facial features, hearing loss, and low calcium levels. Some studies suggest that a loss of the TBX1 gene may also be associated with behavioral problems in affected individuals.
- Testis-specific T-box protein