|
TORSION
DYSTONIA
Torsion Dystonia is a neurological movement disorder
characterised by involuntary contortions of muscles in the neck, torso
and extremities. Occasionally only one of a few muscles are involved.
The disorder is most noticeable when walking. The involvement of
several muscle groups may produce a sideways gait and the body may twist
as if writhing or distorted. There are several types of dystonias that
are characterised by involuntary spasms.
SYMPTOMS
In the early stages of this disorder these muscle
contractions may be mild. They may also be sporadic and occur only
after pronged activity and stress. As the disease progresses, the
painful spasms and contortions begin to occur during physical activity,
particularly walking. In the later stages of the disease, they may also
occur at rest. Not all cases of Torsion Dystonia are progressive and
the muscle spasms may plateau at a mild level. Symptoms may also include
foot drag, cramps in the hands and feet, difficulty in grasping objects
and unclear speech. The contracted tendons and build-up of connective
tissue may cause permanent physical deformities.
CAUSES
Torsion dystonia may be inherited as a recessive,
dominant or X-linked recessive trait. It may also be an acquired
disorder. 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 the 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 the autosomal dominant form of Torsion Dystonia,
the muscles in the torso and the neck are affected first. Symptoms
progress slowly, but new muscle groups may be involved well beyond
adolescence.
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 disorders, is
25%. 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.
In the autosomal recessive form of Torsion Dystonia,
muscle contractions of the feet and hands typically appear in childhood
or adolescence. Symptoms spread quickly to involve the trunk and
extremities, but progression slows after adolescence. This form of the
disorder is usually more severe than the autosomal dominant form.
X-linked recessive disorders are conditions that 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 he 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.
An X-linked recessive form of Torsion Dystonia had
been described in which the initial symptom is spasmodic eye blinking.
A chromosome marker for one hereditary form of
Dystonia has been identified. This 1989 discovery has pointed to the
location of a gene on the long arm of chromosome 9 at q32-34 in one
inherited form of the disease. More research is needed to locate the
exact gene and other genes that cause several types of dystonia and to
develop genetic tests for these disorders.
Torsion Dystonia acquired as result of brain injury
due to infection, trauma, birth injury, or stroke frequently involves
only one side of he body (unilateral) and is generally non-progressive.
AFFECTED POPULATION
The autosomal recessive form of Torsion dystonia
usually becomes apparent by puberty and primarily affects Jews of
Ashkenazi descent. The defective gene is carried by 1:100 Ashkenazic
Jews in the United States. Males and females are affected in equal
numbers.
Onset of the rarer autosomal dominant form is in late
adolescence or early adulthood.
The average age at onset for the X-linked form of
Torsion Dystonia is in the late thirties.
THERAPIES: STANDARD
Torsion Dystonia has been treated with many drugs.
These drugs include Artane (trihexyphenidyl), Cogentin (benztropine),
Valium (diazepam), Rivotril (clonazepam), Lioresal (baclofen), Tegretol
(carbamazepine), Sinemet or Madopar (Levodopa), Parlodel (bromocriptine),
Thorazine (chlorpromazine), Dartral (thiopropozate), Serenace or Haldol
(haloperidol), Orap (pimpozide), Nitoman (tetrabenazine) and Symmetrel (amantadine).
Genetic counselling may be of benefit for patients
and their families.
THERAPIES: INVESTIGATIONAL
Researchers who are investigating Torsion Dystonia
are continuing to search for drugs that may help treat dystonic
symptoms. Investigators are also seeking better surgical techniques,
including the implantation of electrical stimulating devices that may
enhance nerve impulse transmission.
Effectiveness and long-term side effects of these
implanted devices have not been fully documented and more extensive
research is being pursued before their therapeutic value for the
treatment of Torsion Dystonia can be evaluated.
Surgery is rarely used to treat Torsion Dystonia, but
it is occasionally used to destroy cells of the deeply placed grey
matter (basal ganglia) of the brain. It is believed that these are the
cells that are firing off the wrong instructions to the muscles causing
contortions that are characteristic of Torsion Dystonia. It should be
noted that the risk of brain damage from this procedure is very high.
Surgery may also be used in extreme cases to sever nerves leading to the
contracting muscles.
Researchers at the National Institute of Neurological
Disorders and Stroke in Bethesda, MD are testing a Parkinson’s disease
medication, Sinemet, on patients with this form of dystonia. This drug
helps the body to produce dopamine, a naturally occurring chemical in
the brain that is deficient in children with Segawa’s Dystonia.
|
