Amelogenesis Imperfecta

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What is amelogenesis imperfecta?

Amelogenesis imperfecta is a disorder of tooth development. 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, and the defects vary among affected individuals. These problems 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.

How common is amelogenesis imperfecta?

The exact incidence of amelogenesis imperfecta is uncertain. Estimates vary widely, from 1 in 700 people in northern Sweden to 1 in 14,000 people in the United States.

What genes are related to amelogenesis imperfecta?

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 a 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.

Researchers are looking for mutations in other genes that may also cause amelogenesis imperfecta.

How do people inherit amelogenesis imperfecta?

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.

Amelogenesis imperfecta is also inherited in an autosomal recessive pattern; this form of the disorder can result from mutations in the ENAM or MMP20 gene. Autosomal recessive inheritance means two copies of the gene in each cell are altered.

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 an X-linked form of this condition experience more severe dental abnormalities than affected females.

Other cases of this condition result from new gene mutations and occur in people with no history of the disorder in their family.

Source: National Institutes of Health

Researchers' work from University of Ljubljana focuses on life sciences genetics

"Seven different mutations have been identified in the enamelin gene (ENAM). In this paper, we describe the phenotype and ultrastructure of enamel observed using scanning electron microscopy (SEM) in patients with two autosomal dominant (AD) mutations in the ENAM gene: g.13185-13186insAG and g.8344delG, each in one of two unrelated families. Mutations were confirmed by sequence analysis of PCR amplified products of all 10 exons and exon/intron boundaries of the ENAM gene. Phenotypic diversity was observed in patients with ENAM gene mutations g.13185-13186insAG with consecutive protein alteration designated as p.P422fsX488 within family 1. In the proband, the enamel of his entire dentition was chalky white with only mild local hypoplastic alteration, while the phenotypic appearance of his father's dentition was that of local hypoplastic AI. In patients with the ENAM gene mutation g.8344delG from family 2 with consecutive protein alteration designated as p.N197fsX277, generalised hypoplastic AI was observed. Ultrastructural enamel changes in the patient with the autosomal dominant ENAM g.13185-13186insAG mutation, described for the first time in this study, were less pronounced compared to ultrastructural changes in patients with the autosomal dominant ENAM mutation 8344delG," wrote A. Pavlic and colleagues, University of Ljubljana.

The researchers concluded: "Ultrastructural characteristics of the g.13185-13186insAG mutation revealed deformed prisms, an oval shape on the cross-section and wider interprism spaces, while enamel with the ENAM mutation 8344delG was laminated, but prismless."

Pavlic and colleagues published the results of their research in Archives of Oral Biology (Phenotype and enamel ultrastructure characteristics in patients with ENAM gene mutations g.13185-13186insAG and 8344delG. Archives of Oral Biology, 2007;52(3):209-17).

For additional information, contact A. Pavlic, University of Ljubljana, Dept. of Paediatric and Preventive Dentistry, Faculty of Medicine, Hrvatski trg 6, 1000 Ljubljana, Slovenia.

The publisher of the journal Archives of Oral Biology can be contacted at: Pergamon-Elsevier Science Ltd., the Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, England.

Keywords: Slovenia, Ljubljana, Life Sciences Genetics.

This article was prepared by Life Science Weekly editors from staff and other reports. Copyright 2007, Life Science Weekly via NewsRx.com.