Amelogenesis imperfecta

Description, Causes and Risk Factors:

Amelogenesis imperfecta (AI) is a diverse collection of inherited diseases that exhibit quantitative or qualitative tooth enamel defects in the absence of systemic manifestations. This condition causes teeth to be unusually small, discolored, pitted or grooved, and prone to rapid wear and breakage. Other dental abnormalities are also possible. These defects, which vary among affected individuals, can affect both primary (baby) teeth and permanent teeth.

Researchers have described at least 14 forms of amelogenesis imperfecta. These types are distinguished by their specific dental abnormalities and by their pattern of inheritance. The exact incidence of amelogenesis imperfecta is uncertain. Estimates vary widely, from 1 in 700 people in northern Sweden to 1 in 1400 people in the United States.

The amelogenesis imperfecta enamel defects are highly variable and include abnormalities that are classified as hypoplastic (defect in amount of enamel), hypomaturation (defect in final growth and maturation of enamel crystallites), and hypocalcified (defect in initial crystallite formation followed by defective growth). The enamel in both the hypomaturation and hypocalcified AI types is not mineralized to the level of normal enamel and can be described as hypomineralized. Amelogenesis imperfecta can be inherited as an x-linked, autosomal recessive (AR), or autosomal dominant (AD) condition.

The AI trait can be transmitted by either autosomal dominant, autosomal recessive, or X-linked modes of inheritance. Mutations in the AMELX, ENAM, and MMP20 genes cause amelogenesis imperfecta. The AMELX, ENAM, and MMP20 genes provide instructions for making proteins that are essential for normal tooth development. These proteins are involved in the formation of enamel, which is the hard, calcium-rich material that forms the protective outer layer of each tooth. Mutations in any of these genes alter the structure of these proteins or prevent the genes from making any protein at all. As a result, tooth enamel is abnormally thin or soft and may have a yellow or brown color. Teeth with defective enamel are weak and easily damaged.

In some cases, the genetic cause of amelogenesis imperfecta has not been identified. Researchers are working to find mutations in other genes that are responsible for this disorder.

Amelogenesis imperfecta can have different inheritance patterns depending on the gene that is altered. Most cases are caused by mutations in the ENAM gene and are inherited in an autosomal dominant pattern. This type of inheritance means one copy of the altered gene in each cell is sufficient to cause the disorder.

About 5 percent of amelogenesis imperfecta cases are caused by mutations in the AMELX gene and are inherited in an X-linked pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In most cases, males with X-linked amelogenesis imperfecta experience more severe dental abnormalities than females with this form of this condition.

Other cases of amelogenesis imperfecta result from new mutations in these genes and occur in people with no history of the disorder in their family.

Symptoms:

There are a number of symptoms, which include the following.

Thin tooth enamel.

• Soft tooth enamel.

• Pitted tooth enamel.

• Rough tooth enamel.

• The teeth are easily damaged.

• Teeth appear yellow.

Diagnosis:

The diagnosis and classification of AI has traditionally been based on the clinical presentation or phenotype and the inheritance pattern. Although multiple gene defects responsible for causing AI have been identified since 1990, most of the AI types do not have a known molecular basis. As the molecular defects causing AI are identified, the need for a molecular based nomenclature increases. The rapid identification of multiple mutations in multiple genes has lead to the acceptance of standardized nomenclatures for reporting AI associated mutations at the genomic, cDNA and protein level. The most widely accepted classification system for delineating the AI types subdivides AI into four main types based on the enamel defects and then further divides them into14 distinct subtypes based on clinical appearance (phenotype) and mode of inheritance.

X-rays and other imaging scans may be taken during exams to assess the extent of damage to the inner layers of the teeth. Genetic blood testing also may be ordered to confirm that symptoms are the result of an inherited condition rather than poor hygiene or other environmental factors.

Treatment:

Crowns are sometimes being used to compensate for the soft enamel. Usually stainless steel crowns are used in children which may be replaced by porcelain once they reach adulthood. In the worst case scenario, the teeth may have to be extracted and implants or dentures are required.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

Related disease: Tooth Decay