Anodontia is a genetic disorder commonly defined as the absence of all teeth, and is extremely rarely encountered in a pure form without any associated abnormalities. Rare but more common than complete anodontia are hypodontia and oligodontia. Hypodontia is genetic in origin and usually involves the absence of from 1 to 6 teeth. Oligodontia is genetic as well and is the term most commonly used to describe conditions in which more than six teeth are missing.
These conditions may involve either the primary or permanent sets of teeth, but most cases involve the permanent teeth. These phenomena are associated with a group of non-progressive skin and nerve syndromes called the ectodermal dysplasias. Anodontia, especially, is usually part of a syndrome and seldom occurs as an isolated entity.
Anodontia is characterized by partial or complete absence of teeth. Since all primary teeth are usually present by the age of three, their absence is usually noted and a dentist consulted. Except for the wisdom teeth, all permanent teeth are obvious by ages 12 to 14. When teeth have not appeared by the appropriate age, dental X-rays are usually taken.
When anodontia occurs, abnormalities of hair, nails, and sweat glands may also be present. In many cases, anodontia is a component of one of the ectodermal dysplasias, a group of hereditary disorders. (For more information, choose “Ectodermal Dysplasia” as your search term in the Rare Disease Database.)
The complete absence of permanent teeth, anodontia, is extremely rare and is transmitted as an autosomal recessive genetic trait. The location of the faulty gene is not yet known.
The malfunctioning gene causing the autosomal dominant form of hypodontia (HYD1) has been tracked to two separate locations on two separate genes, 14q12-q13 and 4p16.1. The autosomal recessive form (HYD2) has been tracked to a faulty gene at gene map locus 16q12.1.
There appear to be two forms of oligodontia as well. The better-known form is caused by a mutation of a gene located at chromosome14q12-13 and is transmitted as an autosomal dominant trait. The other form, less common and less well known, is caused by a mutation at an unknown location on the X-chromosome.
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 14q12-13” refers to a location between bands 12 and 13 on the long arm of chromosome 14. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry a few abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
X-linked recessive genetic disorders are conditions caused by an abnormal gene on the X chromosome. Females have two X chromosomes but one of the X chromosomes is “turned off” and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is turned off. A male has one X chromosome and if he inherits an X chromosome that contains a disease gene, he will develop the disease. Males with X-linked disorders pass the disease gene to all of their daughters, who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring. Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease, and a 25% chance to have an unaffected son.
X-linked dominant disorders are also caused by an abnormal gene on the X chromosome, but in these rare conditions, females with an abnormal gene are affected with the disease. Males with an abnormal gene are more severely affected than females, and many of these males do not survive.
Anodontia is present at birth. The disorder affects males and females in equal numbers.
Treatment of anodontia consists of artificial dentures. If only front teeth are missing, in hypodontia or oligodontia, a flexible system allowing slight movement of a bridge can be created by bonding an acrylic tooth to the supporting structure (abutments) by means of three orthodontic wires.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
For information about clinical trials sponsored by private sources, contact:
A study sponsored by the National Center for Research Resources is recruiting (2005) individuals with anodontia for a study aimed at identifying the gene or genes responsible for tooth disorders. Further information is available through the NIH recruitment office (see above).
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FROM THE INTERNET
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