CD-ROM Today 1996 January/CD-ROM Today 1996 January.iso/dp/0359/03598.txt

Text File | 1994-01-17 | 10KB | 252 lines

$Unique_ID{BRK03598}
$Pretitle{}
$Title{Choroideremia}
$Subject{Choroideremia Progressive Tapetochoroidal Dystrophy TCD Progressive
Choroidal Atrophy Choroidal Sclerosis X-linked Retinitis Pigmentosa Diffuse
Choriocapillaris Atrophy Gyrate Atrophy of the Choroid and Retina}
$Volume{}
$Log{}

Copyright (C) 1988, 1989, 1991 National Organization for Rare Disorders,
Inc.

525:
Choroideremia

** IMPORTANT **
It is possible the main title of the article (Choroideremia) 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

     Progressive Tapetochoroidal Dystrophy
     TCD
     Progressive Choroidal Atrophy
     Choroidal Sclerosis

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

     X-linked Retinitis Pigmentosa
     Diffuse Choriocapillaris Atrophy
     Gyrate Atrophy of the Choroid and Retina

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.


Choroideremia is a genetic vision disorder which usually affects males.
Female carriers may have mild symptoms without loss of vision.  Major
symptoms include a progressive loss of the central field of vision and night
blindness during childhood.

Symptoms

Choroideremia is characterized by extensive defects in the pigmented surface
layer of cells (epithelium) in the eye.  This disorder usually begins during
childhood with wasting (atrophy) of the retinal layers and choroid of the
eye.  The retina is the light-sensitive, internal coat of the inside of the
eyeball consisting of eight layers.  Seven of these layers contain nerves,
and one layer contains pigmentation.  The choroid is a vascular membrane
located between the retina inside the eye and the "white" section on the
outside the eye (sclera).  The choroid contains large branched pigment cells
and prevents the passage of light rays through areas of the eye outside of
the pupils.  Night blindness is usually the first noticeable symptom, usually
occurring during childhood.

Degeneration of the vessels of the choroid and functional damage to the
retina occur later in life and usually lead to progressive central vision
field loss and eventual blindness.  Tiny bony-like tissue formations and
scattered pigment clumps tend to accumulate in the middle and on the edges of
the choroid.  The symptoms of Choroideremia may vary greatly between affected
individuals.  Female carriers usually have very mild symptoms without vision
loss.

Causes

Choroideremia is inherited as an X-linked trait.  (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.  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 1991 Dr. Fran Cremers of the University of Nijmegen in the Netherlands
isolated the gene believed to be responsible for Choroideremia.  This
discovery will hopefully lead to a prenatal test for the disease.

Affected Population

Choroideremia usually affects males while females may be carriers of the
chromosome defect.  However, a small number of females with the more severe
form of the disorder have been identified.  In the Salla area of northern
Finland an unusually high concentration of cases has occurred, affecting
approximately one in forty persons.

Related Disorders

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

X-linked Retinitis Pigmentosa (RP) is one of a group of inherited vision
disorders causing degeneration of the retina.  When the retina degenerates,
as in RP, the vision decreases and may occasionally be lost.  Retinitis
Pigmentosa may be associated with other conditions or illnesses.  The X-
linked form of RP is passed from a mother (who is a carrier) to a son.  The
early symptoms include night blindness.  This is followed by "tunnel vision"
(loss of peripheral vision).  The rate and extent of progression of symptoms
is extremely variable.  (For more information on this disorder, choose
"Retinitis Pigmentosa" as your search term in the Rare Disease Database).

Diffuse Choriocapillaris Atrophy is characterized by degeneration of the
internal cell layer of the choroid of the eye.  The choroid is a vascular
membrane located between the retina inside the eye and the "white" membrane
outside the eye (sclera), which contains large branched pigment cells and
prevents the passage of light rays through areas outside of the pupil.

Gyrate Atrophy of the Choroid and Retina is characterized by a circular-
patterned degeneration in the choroid and retina of the eye.

Therapies:  Standard

Treatment of Choroideremia is symptomatic and supportive.  Organizations
providing services to sight-impaired people will be of help to patients and
their families.  Genetic counseling is recommended for families affected by
this disorder.

Therapies:  Investigational

Studies of families with Choroideremia are underway to determine the exact
location of the gene responsible for the disorder.  When the location is
discovered, the exact mechanism whereby this progressive loss of vision
develops may become better understood, and new treatments may eventually be
found.

This disease entry is based upon medical information available through
May 1991.  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 Chorodieremia, please contact:

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

     NIH/National Eye Institute (NEI)
     9000 Rockville Pike
     Bethesda, MD  20892
     [phone]

     Eye Research Institute of Retina Foundation
     Macular Disease Research Center
     20 Staniford St.
     Boston, MA  02114
     [phone]

     National Federation of the Blind
     1800 Johnson Street
     Baltimore, MD  21230
     [phone]
     1-800-638-7518

     American Council of the Blind, Inc. (ACB)
     1155 - 15th St., NW, Suite 720
     Washington, D.C.  20005
     [phone]
     [phone]

     American Foundation for the Blind (AFB)
     15 W. 16th St.
     New York, NY  10011
     [phone]
     Regional offices:
     Atlanta, GA  [phone]
     Chicago, IL  [phone]
     Dallas, TX  [phone]
     San Francisco, CA  [phone]


     Vision Foundation, Inc.
     818 Mt. Auburn Street
     Watertown, MA  02172
     [phone]
     1-800-852-3029 (Inside Massachusetts)

     Council of Families with Visual Impairment
     6212 W. Franklin Street
     Richmond, VA  23226
     [phone]

     National Association for Parents of the Visually Impaired, Inc. (NAVPI)
     P.O. Box 180806
     Austin, TX  78718
     [phone]

     National Association for the Visually Handicapped (NAVH)
     305 East 24th Street
     New York, NY  10010
     [phone]
     or
     3201 Balboa Street
     San Francisco, CA  94121
     [phone]

     National Library Service for the Blind and Physically Handicapped
     Library of Congress
     1291 Taylor Street NW
     Washington, DC  20542
     [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 Rare Disease Database entry is based upon outlines prepared by medical
and dental students (1984-1986) at the Medical College of Virginia for their
course in human genetics, and the following articles:

MENDELIAN INHERITANCE IN MAN, 7th ed.:  Victor A. McKusick; Johns Hopkins
University Press, 1986.  Pp. 1336.

MULTIPOINT LINKAGE ANALYSIS OF LOCI IN THE PROXIMAL LONG ARM OF THE HUMAN
X CHROMOSOME:  APPLICATION OF MAPPING THE CHOROIDEREMIA LOCUS:  J.G. Lesko, et
al.; Am J Hum Genet (April 1987, issue 40(4)).  Pp. 303-311.

CHOROIDEREMIA-LOCUS MAPS BETWEEN DXS3 AND DXS11 ON Xq:  A. Gal, et al.;
Hum Genet (June 1986, issue 73(2)).  Pp. 123-126.

HISTOPATHOLOGIC OBSERVATIONS IN CHOROIDEREMIA WITH EMPHASIS ON VASCULAR
CHANGES OF THE UVEAL TRACT:  J.D. Cameron, et al.; Ophthalmology (February
1987, issue 94(2)).  Pp. 187-196.