What is Amelogenesis Imperfecta?

Amelogenesis imperfecta (AI) refers to a group of rare, inherited disorders characterized by abnormal enamel formation, which is the hard, calcium-rich material that forms the protective outer layer of each tooth. The condition causes teeth to to be unusually small, discolored, pitted or grooved, and prone to rapid wear and breakage. The exact incidence of amelogenesis imperfecta is uncertain. Estimates vary widely around the world. In the United States, the number is estimated at 1 in 14,000.

Mutations in genes can cause amelogenesis imperfecta. We currently know that the AMELX, ENAM, MMP20 and FAM83H genes provide instructions for making proteins that are essential for normal tooth development. Mutations in any of these genes can lead to altered protein structures or lack of proteins resulting in teeth with defective or missing enamel.

Depending on the gene that is altered, different inheritance patterns will result. In an autosomal dominant disorder, the mutated gene is a dominant gene located on one of the nonsex chromosomes (autosomes). You need only one mutated gene to be affected by this type of disorder. A person with an autosomal dominant disorder for AI, for example, a father or mother, has a 50/50 chance of having an affected child depending on whether they pass on their dominant (mutated) gene or their recessive (normal) gene.

About 5 percent of amelogenesis imperfecta cases are caused by mutations in the AMELX gene and are inherited in a X-linked pattern where the mutated gene is located on the X chromosome, one of the two sex chromosomes. In this case, a father (XY) will pass the mutated gene to each daughter but not to a son as he will give his daughters the X chromosome with the mutated gene, but his son the Y chromosome. A mother (XX) will have a 50/50 chance of passing the gene to each child depending on whether she gives them the X chromosome with the mutated gene or the normal gene.

There is much yet to be learned about this condition. If you would like to help, please reach out below.