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$Unique_ID{BRK03620}
$Pretitle{}
$Title{Cone Dystrophy}
$Subject{Cone Dystrophy Combined Cone-Rod Degeneration Cone-Rod Degeneration
Cone-Rod Degeneration Progressive Cone-Rod Dystrophy Retinal Cone Degeneration
Retinal Cone Dystrophy Retinal Cone-Rod Dystrophy Flecked Retina Syndrome
Leber's Optic Atrophy Macular Degeneration Oguchi's Disease Retinitis
Pigmentosa X-linked Juvenile Retinoschisis}
$Volume{}
$Log{}

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

847:
Cone Dystrophy

** IMPORTANT **
It is possible that the main title of the article (Cone Dystrophy) is not
the name you expected.  Please check the SYNONYM listing to find the
alternate name and disorder subdivisions covered by this article.

Synonyms

     Combined Cone-Rod Degeneration
     Cone-Rod Degeneration
     Cone-Rod Degeneration, Progressive
     Cone-Rod Dystrophy
     Retinal Cone Degeneration
     Retinal Cone Dystrophy
     Retinal Cone-Rod Dystrophy

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

     Flecked Retina Syndrome
     Leber's Optic Atrophy
     Macular Degeneration
     Oguchi's Disease
     Retinitis Pigmentosa
     X-linked Juvenile Retinoschisis

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.

Cone Dystrophy is a rare disorder of the eye that is usually inherited.
However there have been numerous reports of cases appearing for no apparent
reason.  The cells that receive light stimuli (cone cells and rod cells) in
the retina of the eye deteriorate causing impaired vision.  This disorder
normally occurs during the first to third decades of life.

Symptoms

Symptoms of Cone Dystrophy may include impaired central vision (vision
directly ahead), faulty color vision (usually red-green or blue-yellow
defects), day blindness (vision decreases in good light), and a rapid or
jerky movement of the eyeball (nystagmus).

Some patients may have lesions in the middle of the retina known as
"Bull's Eye" macular lesions and there may be a lack of color in the optic
disc (the "blind spot" or part of the eye with no light receptors).

When Cone Dystrophy is associated with an X-linked inheritance, the
patient may have a golden yellow sheen throughout the retina and become blind
due to dark spots in the visual field.  This X-linked form of the disorder
only occurs in males.  Female carriers of the gene occasionally show
extremely mild features of the disorder.

Causes

Cone Dystrophy may occur for no apparent reason or be caused by X-linked
recessive, autosomal dominant or autosomal recessive inheritance.  The most
common cause of this disorder is autosomal recessive inheritance.

Human traits including the classic genetic diseases, are the product of
the interaction of two genes, 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 other normal
gene and resulting in the appearance of the disease.  The risk of
transmitting the disorder from affected parent to offspring is fifty percent
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 for the same trait 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 not show 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 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 only have 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.

Affected Population

Cone Dystrophy affects males and females equally when there is an autosomal
dominant or autosomal recessive inheritance.  Males and females are equally
affected when the disorder occurs sporadically.  However, when Cone Dystrophy
is inherited as an X-linked disorder it affects only males although female
carriers can show mild symptoms.  The X-linked form of the disorder the
rarest.

The symptoms of Cone Dystrophy usually present themselves between the
first and third decades of life.

Related Disorders

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

Flecked Retina Syndrome is a rare disorder that is characterized by
reduced vision and impaired night vision in some cases.  The area behind the
retinal vessels appears to be marked with white or yellow flecks when an
ophthalmologist looks at it.  This disorder is usually autosomal recessive
and affects both sexes equally.  (For more information on this disorder,
choose "Leber's Optic Atrophy " as your search term in the Rare Disease
Database).

Leber's Optic Atrophy is a rare genetic disorder of the eye.  This
disorder is characterized by a slow loss of vision usually beginning around
the second decade.  Leber's Optic Atrophy is marked by slow degeneration of
cells in the retina causing reduced vision or blindness.  This disorder is
inherited as an autosomal recessive trait.  (For more information on this
disorder choose "Lebers Optic Atrophy" as your search term in the Rare
Disease Database).

Macular Degeneration is a hereditary disorder of the eye.  This
progressive disorder is characterized by a gradual loss of vision usually in
both eyes.  The primary symptoms of Macular Degeneration include perception
of unclear shapes and blind spots within the field of vision.  (For more
information on this disorder choose "Macular Degeneration" as your search
term in the Rare Disease Database).

Oguchi's Disease is also known as hereditary night-blindness and may be
associated with vitamin A deficiency.  This nonprogressive disorder occurs
predominantly in Japan and usually begins in infancy.  The main symptom of
this disorder is limited vision in dim light.  (For more information on this
disorder choose "Leber's Optic Atrophy" as your search term in the Rare
Disease Database).

Retinitis Pigmentosa is an inherited disorder that causes degeneration of
the retina.  One of the earliest symptoms is difficulty seeing at night or in
dimly lit places.  This symptom is slowly followed by tunnel vision.  The
rate and extent of progression varies greatly.  (For more information on this
disorder choose "Retinitis Pigmentosa" as your search term in the Rare
Disease Database).

X-linked Juvenile Retinoschisis is a rare genetic disorder that affects
males.  The major symptoms are poor eyesight and degeneration of the retina.
Often this disorder is associated with the development of cysts (saclike
blisters) in the retina.  Other symptoms may include detachment of all or
part of the retina from the rest of the eye and wasting away of the choroid
(the membrane between the white part of the eye and the retina).  (For more
information on this disorder choose Juvenile Retinoschisis as your search
term in the Rare Disease Database).

Therapies:  Standard

Diagnosis of Cone Dystrophy can be made by an ophthalmologist through various
tests:

An ERG (electroretinogram) may be used to indicate abnormalities in the
retina.  This device records the electrical impulses given off by the retina
in response to light stimulus.

An EOG (electro-oculography) may be performed in order to determine the
function of the retina, especially the nerve cells that respond to
stimulation from light.

Routine care from an ophthalmologist is required.  Visual aids may help
as vision decreases.  Eye glasses such as Corning 550 CPF are used to protect
the eye from excess light.

Genetic counseling may be of benefit for patients and their families.
Other treatment is symptomatic and supportive.

Therapies:  Investigational

Researchers at the Cullen Eye Institute of the Baylor College of Medicine in
Houston, Texas are studying inherited retinal diseases.  Families with at
least two affected members and both parents living are needed to participate
in this program.

     Dr. Richard Lewis M.D.
     6501 Fannin Suite NC 206
     Cullen Eye Institute, Baylor College of Medicine
     Houston, Texas  77030
     [phone]

This disease entry is based upon medical information available through
June 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

     National Organization for Rare Disorders (NORD)
     P.O. Box 8923
     New Fairfield, CT  06812-1783
     203-746-6518

     RP Foundation Fighting Blindness
     1401 Mt. Royal Avenue, 4th Floor
     Baltimore, MD  21217
     800-638-2300
     301-255-9400
     TDD 301-225-9409

     Association for Macular Disease, Inc.
     210 East 64th Street
     New York, NY  10021
     [phone]

     NIH/National Eye Institute
     9000 Rockville Pike
     Bethesda, MD  20892
     301-496-5248

For genetic information and Genetic Counseling Referrals:

     March of Dimes Birth Defects Foundation
     1275 Mamaroneck Avenue
     White Plains, NY 10605
     914-428-7100

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

References

MENDELIAN INHERITANCE IN MAN, 9th Ed.:  Victor A. McKusick, Editor; Johns
Hopkins University Press, 1990.  Pp. 223, 829, 1109, 1580, 1581.

BIRTH DEFECTS ENCYCLOPEDIA, Mary Louise Buyse, M.D., Editor-In-Chief;
Blackwell Scientific Publications, 1990.  Pp. 1475-1476.

CLINICAL OPHTHALMOLOGY, 2nd Ed.; Jack J. Kanski, Editor; Butterwor, 1990.
Pp. 376-377.

PRINCIPLES OF NEUROLOGY, 4th Ed.; Raymond D. Adams, M.D. and Maurice
Victor, M.D., Editors; McGraw-Hill Information Services Company, 1989.  P.
204.

AUTOSOMAL DOMINANTLY INHERITED MACULAR DYSTROPHY WITH PREFERENTIAL SHORT-
WAVELENGTH SENSITIVE CONE INVOLVEMENT:  G.H. Bresnick et al.; Am J Ophthalmol
(1989:  issue 108(3)).  Pp.  265-76.

THE GOLDEN TAPETAL SHEEN REFLEX IN RETINAL DISEASE:  K.G. Noble et al.;
Am J Ophthalmol (1989:  issue 107(3)).  Pp.  211-7.

PROGRESSIVE PERIPHERAL CONE DYSFUNCTION:  K.G. Noble et al.; Am J
Ophthalmol (1988:  issue 106(5)).  Pp.  557-60.

CONE DYSTROPHY.  PHENOTYPIC DIVERSITY BY RETINAL FUNCTION TESTING:  K.
Yagasaki et al.; Arch Ophthalmol (1989:  issue 107(5)).  Pp.  701-8.