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$Unique_ID{BRK03839}
$Pretitle{}
$Title{Hyperexplexia}
$Subject{Hyperexplexia Kok Disease Exaggerated Startle Reaction Startle
Disease Hyperekplexia Familial Startle Disease Jumping Frenchmen of Maine
Startle Epilepsy }
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$Log{}

Copyright (C) 1990 National Organization for Rare Disorders, Inc.

816:
Hyperexplexia

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

Synonyms

     Kok Disease
     Exaggerated Startle Reaction
     Startle Disease
     Hyperekplexia
     Familial Startle Disease

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

     Jumping Frenchmen of Maine
     Startle Epilepsy

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.

Hyperexplexia is a rare hereditary neurological disorder.  Individuals
with this disorder have an excessive startle reaction to sudden unexpected
noise, movement, or touch.  Symptoms include extreme muscle tension sometimes
causing stiffness (hypertonia), and falling stiffly (like a log) to the
ground without loss of consciousness.  Exaggeration of reflexes
(hyperreflexia), and an unstable gait may also occur.

Symptoms

There is a major and minor form of Hyperexplexia.  In the major form,
Hyperexplexia is characterized by an unusually extreme startle reaction to
sudden unexpected noise, movement, or touch.  Arching of the head, jerking
movements (myoclonic jerks) or falling stiffly to the ground (like a log)
without loss of consciousness tend to occur when the individual is startled.
Jerking movements can also occur when the patient is trying to fall asleep
(nocturnal myoclonic jerks).  (For more information on myoclonic jerks,
choose "myoclonus" as your search term in the Rare Disease Database).

Extreme muscle tension or stiffness (hypertonia) is common in infants with
Hyperexplexia.  Individuals with Hyperexplexia may not move around much; when
they do, they may move slowly (hypokinesia).  Other symptoms may include
exaggeration of reflexes (hyperreflexia), interrupted breathing (intermittent
apnea) and/or unstable walking (gait).  Some patients have a dislocation of
the hip which is present at birth.  Hernias may occur in the lower abdomen
(inguinal hernias).

In its minor form, individuals with Hyperexplexia usually experience only
an inconstant exaggerated startle reaction with few or none of the other
symptoms.  In infants with the minor form, the reaction may be brought on by
fever.  In children and adults, intensity of the startle response may be
affected by stress or anxiety.

Onset of both major and minor forms of Hyperexplexia is usually from
birth, but in some patients it does not occur until adolescence or adulthood.

Some researchers believe there is a sporadic form of Hyperexplexia as
well as a hereditary form.  Others disagree; they believe that there is only
a hereditary form and that it was either misdiagnosed in the past or occurred
with a late onset of symptoms.

Causes

Hyperexplexia is inherited as an autosomal dominant trait.  In some cases,
there is a hereditary male-to-male transmission.  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
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.

Affected Population

Hyperexplexia is a rare genetic disorder present at birth.  It affects both
males and females.  Onset of the disorder is usually from birth but in some
individuals it may not occur until adolescence or adulthood.

Related Disorders

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

Jumping Frenchmen of Maine is a disorder characterized by an extreme
startle reaction consisting of jumping, raising the arms, yelling, hitting,
obeying sudden commands, or involuntarily repeating sentences.  (People with
Hyperexplexia do not have the imitative repetition of words or actions, or
the forced obedience response found in "Jumping Frenchmen").  The intensity
of the response may be affected by the frequency of being startled, fatigue
and/or stress.  The affected person must be startled by an unexpected event
in order to elicit the reaction.  It is suspected to be a genetic disorder
and/or an extreme conditioned response to a particular situation possibly
influenced by cultural factors.  (For more information on this disorder,
choose "Jumping Frenchmen" as your search term in the Rare Disease Database).

Startle Epilepsy is expressed as a brief muscular contraction
predominating on one-half of the body in response to sudden noise or
movement.  These patients often fall when startled and also have other
seizure manifestations.  (For more information on this disorder, choose
"Epilepsy" as your search term in the Rare Disease Database).

Therapies:  Standard

Testing for Hyperexplexia can include electromyograms (records of electrical
impulses produced by the muscles) and electroencephalograms (EEG, or records
of electrical activity in the brain).  Treatment of Hyperexplexia includes
the drugs clonazepam, valproic acid, 5-hydroxytryptophan, or piracetam.

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

Therapies:  Investigational

This disease entry is based upon medical information available through
November 1990.  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 Hyperexplexia, please contact:

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

     NIH/National Institute of Neurological Disorders & Stroke (NINDS)
     9000 Rockville Pike
     Bethesda, MD  20892
     [phone]
     [phone]

For genetic information and genetic counseling referrals:

     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

MENDELIAN INHERITANCE IN MAN, 8th Ed.:  Victor A. McKusick; Johns Hopkins
University Press, 1986.  Pp. 445-446.

HYPEREXPLEXIA:  AN INHERITED DISORDER OF THE STARTLE RESPONSE.  D. J.
Morley, et al.; Clin Genet (Jun 1982; issue 21 (6)).  Pp. 388-396.

HYPEREKPLEXIA.  T.W. Kurczynski; Arch Neurol (Apr 1983; issue 40 (4)).
Pp. 246-248.

HYPEREXPLEXIA:  A SYNDROME OF PATHOLOGICAL STARTLE RESPONSES.  E. Saenz-
Lope, et al.; Ann Neurol (Jan 1984; issue 15 (1)).  Pp. 36-41.

STARTLE DISEASE OR HYPEREXPLEXIA:  FURTHER DELINEATION OF THE SYNDROME.
F. Andermann, et al.; Brain (Dec 1980; issue 103 (4)).  Pp. 985-997.

STARTLE DISEASE OR HYPEREXPLEXIA:  ADOLESCENT ONSET AND RESPONSE TO
VALPROATE.  J. M. Dooley and F. Andermann; Pediatr Neurol (Mar-Apr 1989;
issue 5 (2)).  Pp. 126-127.