Congenitally missing teeth can be attributed to genetic defects. One of the genes that is most likely to contribute to this is the PAX 9 gene. The defects that lead to the failure of certain teeth to develop can be the result of something as simple as a point mutation that changes one amino acid in the genetic sequence. In this study a family of four, with congenitally missing teeth, was examined for a mutation in the PAX 9 gene. A homozygous mutation in the PAX9 gene was found in exon 3 altering the amino acid sequence. The mutation which causes the protein to express an alanine instead of a proline, leads to a change in the helical structure of the protein. This mutation is likely a contributing factor to the cause of the congenitally missing teeth shown in the father, mother and two children of this family.