CD-ROM Today 1996 January/CD-ROM Today 1996 January.iso/dp/0345/03450.txt

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$Unique_ID{BRK03450}
$Pretitle{}
$Title{Amelogenesis Imperfecta}
$Subject{Amelogenesis Imperfecta Brown Enamel, Hereditary Hypocalcified
(Hypomineralized) Type Hypomaturation Type (Snow-Capped Teeth) Taurodontism
Hypoplastic (Hypoplastic-Explastic) Type}
$Volume{}
$Log{}

Copyright (C) 1988, 1989 National Organization for Rare Disorders, Inc.

501:
Amelogenesis Imperfecta

** IMPORTANT **
It is possible the main title of the article (Amelogenesis Imperfecta) is
not the name you expected.  Please check the SYNONYMS listing on the next
page to find alternate names and disorder subdivisions covered by this
article.

Synonyms

     Brown Enamel, Hereditary

Includes:

     Hypocalcified (Hypomineralized) Type
     Hypomaturation Type (Snow-Capped Teeth)
     Hypoplastic (Hypoplastic-Explastic) Type

Information on the following diseases can be found in the Related
Disorders section of this report:

     Taurodontism
     Tricho-Dento-Osseous Syndrome
     General Discussion

** REMINDER **
The information contained in the Rare Disease Database is provided for
educational purposes only.  It should not be used for diagnostic or treatment
purposes.  If you wish to obtain more information about this disorder, please
contact your personal physician and/or the agencies listed in the "Resources"
section of this report.

Amelogenesis Imperfecta is a rare genetic disorder characterized by a
developmental defect of the tooth enamel.  Clinical and X-ray findings will
vary between the different types of Amelogenesis.

Symptoms

Amelogenesis Imperfecta is characterized by defective or missing tooth
enamel.  Secondary effects of this disorder may be early tooth loss,
heightened susceptibility to disease of the tissues surrounding the teeth
(periodontal) such as gums, cement, ligaments, and the bone in which the
tooth root rests (alveolar).  Sensitivity of the teeth to hot and cold is
usually increased.  The dental pulp (pulpa) in the root canal is exposed in
some cases, and a so-called "open bite" may occur because the upper and
lower jaws do not align properly.  Another complication of Amelogenesis
Imperfecta is that the unsightly teeth may cause psychological problems.
With orthodontic and periodontal restoration, however, the teeth will look
normal and can remain functional throughout life.

The disorder occurs in the following forms:

HYPOCALCIFIED TYPE
Unerupted and newly erupted teeth in affected children are covered by a
light yellow-brown enamel.  After eruption, the enamel turns brown or black
from food stains.  The enamel crumbles easily and wears off rapidly, so by
the age of 10-12 years only the cores of the teeth consisting of dentin
remain.  Enamel of the neck (cervical) portion of the teeth may be better
calcified.  Upper and lower front jaws often do not close completely
resulting in an "anterior open bite".  The teeth are overly sensitive to
temperature changes.  On X-ray photos, the enamel appears less dense than the
dentin of the core.  The crown of the affected teeth appears to have small
irregular holes, with a dense line of calcified enamel at the neck of the
tooth.  Symptoms are more severe in the autosomal recessive form than in the
autosomal dominant form of this type of Amelogenesis Imperfecta.

Pigmented Autosomal Recessive Hypomaturation Type:
The enamel is clear to cloudy light brown and of normal thickness.
However, the enamel tends to break off from the dentin core.  The enamel is
softer than normal and can be penetrated by a sharp dental instrument.  X-ray
photos show a lack of contrast between enamel and dentin.

Sex-Linked Autosomal Recessive Hypomaturation Type
In males:
The enamel of the baby (primary) teeth looks white and appears like
ground glass.  The enamel of the permanent teeth appears mottled and yellow.
The soft enamel can be penetrated by a sharp dental instrument under
pressure.

In females:
The enamel of the baby teeth shows vertical bands of abnormal "ground
glass white" enamel randomly alternating with bands of translucent normal
enamel.  The enamel of the permanent teeth shows vertical bands of either
opaque white or opaque yellow enamel randomly alternating with bands of
translucent normal enamel.

HYPOPLASTIC TYPES include:
Pitted Autosomal Dominant Hypoplastic Type:
The enamel is thin with random pits from pinpoint to pinhead size primarily on
the surfaces of permanent teeth facing the lips or cheeks (labial or buccal).
Some teeth may be normal in both baby and permanent teeth.  X-ray photos show
a normal contrast between the enamel and the dentin core of the teeth.

Rough Autosomal Dominant Hypoplastic Type:
The enamel is thin, brown, and very hard, with a grainy glassy (granular
vitreous) surface.  There is lack of contact between adjacent teeth.  On X-
ray photos, the teeth appear outlined by a thin layer of enamel.  A high
contrast between enamel and dentin can be noticed.

Rough Autosomal Recessive Hypoplastic Type:
The tooth surface is rough, grainy, and light yellow-brown in color.  Lack of
contact between adjacent teeth occurs.  X-ray photos show no enamel present.
Many teeth are unerupted and partially resorbed into the jaws.
Microscopically, the only evidence of enamel is the laminated agate-like
glassy calcification on the surface of the tooth core.

Smooth Autosomal Dominant Hypoplastic Type:
The enamel is thin, brown, smooth, and glossy, except where it is not
calcified properly (hypocalcified) at contact points.  Lack of contact occurs
between adjacent teeth.  X-ray photos show many unerupted teeth with
resorption of the crowns in the jaw bones.  Small calcified spots may be seen
adjacent to unerupted teeth.

Local Autosomal Dominant Hypoplastic Type:
Only the baby teeth may be affected.  Pits and grooves of underdeveloped
(hypoplastic) enamel occur horizontally across the middle third of a tooth.
Defective enamel may be present in all or only some of the teeth.  The most
frequently affected teeth are the incisors, or the baby molars.

Sex-Linked Dominant Hypoplastic Type:
Males:
The enamel is thin, brown or yellow-brown, smooth, and shiny.
Females:
Alternating vertical bands of normal and abnormal enamel (Lyon effect)
occur.   These bands are visible on X-ray photos of the teeth.

Causes

Amelogenesis Imperfecta is inherited through various modes of transmission.
The Hypomaturation Type is inherited through either autosomal recessive or
sex-linked recessive genes.  The Hypoplastic Type of Amelogenesis Imperfecta
is inherited through either autosomal dominant, autosomal recessive, or sex-
linked dominant genes.

Human traits including the classic genetic diseases, are the product of
the interaction of two genes for that condition, one received from the father
and one from the mother.

In dominant disorders, a single copy of the disease gene (received from
either the mother or father) will be expressed "dominating" the normal gene
and resulting in appearance of the disease.  The risk of transmitting the
disorder from affected parent to offspring is 50% for each pregnancy
regardless of the sex of the resulting child.)

In recessive disorders, the condition does not appear unless a person
inherits the same defective gene from each parent.  If one receives one
normal gene and one gene for the disease, the person will be a carrier for
the disease, but usually will show no symptoms.  The risk of transmitting the
disease to the children of a couple, both of whom are carriers for a
recessive disorder, is twenty-five percent.  Fifty percent of their children
will be carriers, but healthy as described above.  Twenty-five percent of
their children will receive both normal genes, one from each parent and will
be genetically normal.

X-linked recessive disorders are conditions which are coded on the X
chromosome.  Females have two X chromosomes, but males have one X chromosome
and one Y chromosome.  Therefore in females, disease traits on the X
chromosome can be masked by the normal gene on the other X chromosome.  Since
males have only one X chromosome, if they inherit a gene for a disease
present on the X, it will be expressed.  Men with X-linked disorders transmit
the gene to all their daughters, who are carriers, but never to their sons.
Women who are carriers of an X-linked disorder have a fifty percent risk of
transmitting the carrier condition to their daughters, and a fifty percent
risk of transmitting the disease to their sons.)

In X-linked dominant disorders the female with only one X chromosome
affected will develop the disease.  However the affected male always has a
more severe condition.  Sometimes affected males die before birth so that
only female patients survive.

The structural defect in enamel formation during development of the
embryo is thought to be the result of the inhibition of crystallization in
the region between the enamel rods (interrod) related to the development of
the skull and face (craniofacial).  Poor oral hygiene can aggravate symptoms
of Amelogenesis Imperfecta.

Affected Population

Amelogenesis Imperfecta affects between 1 out of 14,000 to 16,000 children in
the United States.  Of this number about 40% have the Hypocalcified Dominant
Type.  The autosomal dominant and recessive forms of the disorder affect
males and females in equal numbers.  The sex-linked dominant type of the
disorder affects twice as many males as females.  The sex-linked recessive
type affects only males.

Related Disorders

Symptoms of the following disorders can be similar to those of Amelogenesis
Imperfecta.  Comparisons may be useful for a differential diagnosis:

Taurodontism (Bull Teeth) is a genetic disorder whose exact mechanism of
inheritance is not known.  The disorder is characterized by large cavities in
the jaw bones in which the tooth pulp rests.  Molars are usually the most
severely affected.  The bull (taurodont) tooth lies deep in the bone.  This
disorder was frequently found in early man and is most often found today in
Eskimos who use their teeth for cutting hides.  Taurodontism may be a form of
Tricho-Dento-Osseous Syndrome.

Tricho-Dento-Osseous Syndrome (TDO Syndrome) is one of a group of
congenital disorders known as the Ectodermal Dysplasias.  Intelligence and
life span are usually normal for individuals with this disorder.  The
condition primarily affects the hair which is strikingly curly, and the
teeth.  X-ray examination of persons with TDO Syndrome usually shows a mild
increase in bone density, particularly in the skull.  Thin and brittle
fingernails also occur.  Children with this disorder may have to wear
dentures.  A person with TDO Syndrome may have Amelogenesis Imperfecta as
well.  (For more information on this disorder, choose "TDO" as your search
term in the Rare Disease Database.)

Therapies:  Standard

Diagnosis of Amelogenesis Imperfecta is usually made by X-ray examination at
the time the teeth erupt.  By 1 to 2 years of age, the diagnosis can be made
by visual examination.

Full crown restorations and a type of denture that caps defective teeth
and corrects "open bite" are excellent treatments for this disorder.
Desensitizing toothpaste can prevent painful sensitivity to heat and cold.
Good oral hygiene is important.

Genetic counseling is recommended for families of children with
Amelogenesis Imperfecta.

Therapies:  Investigational

This disease entry is based upon medical information available through May
1988.  Since NORD's resources are limited, it is not possible to keep every
entry in the Rare Disease Database completely current and accurate.  Please
check with the agencies listed in the Resources section for the most current
information about this disorder.

Resources

For more information on Amelogenesis Imperfecta, please contact:

     National Organization for Rare Disorders (NORD)
     P.O. Box 8923
     New Fairfield, CT  06812-1783
     [phone]

     National Foundation for Ectodermal Dysplasias
     219 E. Main St.
     Mascoutah, IL  62258
     [phone]

     NIH/National Institute of Dental Research
     9000 Rockville Pike
     Bethesda, MD  20892
     [phone]

For genetic information and genetic counseling referrals, please contact:

     March of Dimes Birth Defects Foundation
     1275 Mamaroneck Avenue
     White Plains, NY  10605
     [phone]

     Alliance of Genetic Support Groups
     35 Wisconsin Circle, Suite 440
     Chevy Chase, MD  20815
     (800) 336-GENE
     [phone]

References

This report in the Rare Disease is based on outlines prepared by medical and
dental students (1984-1986) at the Medical College of Virginia for their
course in human genetics.

A NEW CLASSIFICATION OF HERITABLE HUMAN ENAMEL DEFECTS AND A DISCUSSION
OF DENTIN DEFECTS:  E.D. Shields;  Birth Defects (1983:  issue 19(1)).  Pp.
107-127.

A CLINICAL, GENETIC, AND ULTRASTRUCTURAL STUDY OF SNOW-CAPPED TEETH:
AMELOGENESIS IMPERFECTA, HYPOMATURATION TYPE:  V.H. Escobar, et al.;  Oral
Surgery (December 1981:  issue 52(6)).  Pp. 607-614.

AN INVESTIGATION OF THE ASSOCIATION BETWEEN ANTERIOR OPEN-BITE AND
AMELOGENESIS IMPERFECTA:  R. Rowley, et al.;  American Journal Orthod
Dentofacial Orthop (March 1982:  issue 81(3)).  Pp. 229-235.

MODIFIED OVERDENTURES FOR THE MANAGEMENT OF OLIGODONTIA AND DEVELOPMENTAL
DEFECTS:  B.J. Abadi, et al.;  ASDC Journal Dent child (March-April 1982:
issue 49(2)).  Pp. 123-126.