Familial human hypodontia--is it all in the genes?

The congenital absence of teeth is one of the commonest developmental abnormalities seen in human populations. Familial hypodontia or oligodontia represents an absence of varying numbers of primary and/or secondary teeth as an isolated trait. While much progress has been made in understanding the developmental basis of tooth formation, knowledge of the aetiological basis of inherited tooth loss remains poor. The study of mouse genetics has uncovered a large number of candidate genes for this condition, but mutations in only three have been identified in human pedigrees with familial hypodontia or oligodontia: MSX1, PAX9 and AXIN2. This suggests that these conditions may represent a more complex multifactorial trait, influenced by a combination of gene function, environmental interaction and developmental timing. Completion of the human genome project has made available the DNA sequence of the collected human chromosomes, allowing the localisation of all human genes and, ultimately, determination of their function. Therefore it is likely that our understanding of this complex developmental process will continue to improve, not only during normal development but also when things go wrong.