Basal Ganglion and Motor Deficits

Amy Wallace
Psych. 472
Prof. Morgan
11/15/99 

     In 1817, a physician and surgeon named James Parkinson published a short 
paper entitled, “An Essay on the Shaking Palsy.”  Practicing in London, he 
was studying six patients who all demonstrated similar symptoms.  He 
described their characteristics as: “Involuntary tremulous motion, with 
lessened muscular power, a propensity to bend the trunk forwards.” Over a 
century later, the disease that bares his name affects approximately 0.15% of 
the population.(1,2)  
     Until the latter part of the 18th century, symptoms were seen largely as 
entities.  Similarities between specific physical and cognitive disabilities 
were not usually correlated and categorized as a particular illness.  Given 
that and the fact that medical science had not yet implemented the 
stethoscope or reflex hammer, his observation is quite prodigious.  He also 
deserves acknowledgment for recognizing patients with different symptoms were 
suffering from the same disorder at different stages.
     In 1867, a founder of modern neurology named Jean Marie Charcot, 
considerably added to the description of Parkinson’s, including muscular 
rigidity and various other manifestations.  He started treatment with an 
alkaloid drug derived from a plant, which remained the only medical treatment 
for Parkinson’s Disease until nearly a century later.  The origin of the 
disease remained enigmatic for many years; some physicians thought the 
problem was in the muscles, some in the spinal cord, and some believed it to 
be in the brain, but did not know exactly where.  Finally, in 1915, a student 
named Tretiadoff published a thesis describing a number of changes in the 
nerve cells in the substantia nigra, which is a cluster of darkly pigmented 
neurons near the brainstem.  His ideas were controversial, until a group of 
doctors in Sweden discovered nerve pathways that started in the substantia 
nigra and spread to the stratium (a group of nerve cells located in each 
cerebral hemisphere that is essential to muscular movement.)  Using new 
technology, the Swedish researchers found that dopamine was present in both 
areas of the brain.(1) By 1957, Parkinson’s Disease was understood to be a 
state of cerebral dopamine insufficiency.  
     Dopamine is a chemical that can be made in the body (where it functions 
as a hormone) and in the brain (where it functions as a neurotransmitter.)  A 
neurotransmitter is a chemical that must be present in the synapse between a 
neuron’s receiving and transmitting structures, the dendrite and axon, in 
order for the electrical impulse to transmit from one area to another.  There 
is no direct passageway from the brain to the muscles; nerve impulses must 
travel through the spinal cord and into the peripheral nervous system (PNS).  
The connection between the motor nerve cells in the spinal cord and the PNS 
nerve cells is usually not impaired in Parkinson’s victims.  The neurons in 
the brain and spinal cord would also be able to function except for the 
absence of the essential element dopamine.
     Neurotransmitters are manufactured in the neurons that send their 
signals to receiving cells. That is, the neuron that delivers the impulse 
provides the needed neurotransmitter.  In Parkinson’s, the greatest 
deficiency of dopamine is in the stratium, an important division of the basal 
ganglia, which is a group of neurons largely responsible for motor control. 
The substantia nigra sends its axons into the stratium.  The nerves in the 
substantia nigra are darkly pigmented and their primary function is to 
produce dopamine.  Over the course of the illness, these cells become less 
pigmented and die.  In the beginning of the disease, the remaining cells work 
overtime attempting to make up for the neurons which have already died, but 
eventually they reach a point where they cannot produce enough dopamine to 
keep the stratium functioning.  This leads to disturbances in the ability of 
the stratium to operate and results in physical and sometimes mental 
disturbances.
     The exact purpose of the stratium is not fully understood, yet it is 
generally accepted that it sends out and receives messages from almost all 
centers in the nervous system.  The nigrostriam (the substantia nigra and 
stratium represented together) has two main responsibilities.  First, it must 
coordinate a series of muscular movements required in any action.  Second, it 
is responsible for maintaining muscular tone.  The stratium organizes all 
nerve impulses responsible for any movement such as walking, brushing one’s 
hair, or playing a musical instrument.   Parkinson’s diminishes tone in the 
extensor muscles, which are the muscles on the exterior of the body that 
control extension and straightening.(3)  
This creates a variety of ailments, usually appearing first as a slight 
tremor, commonly in the hands.  “Pin rolling” is a typical symptom wherein 
the patient seems to be rolling a pill between their thumb and index finger.  
(Such involuntary tremors increase during relaxation, but subside while the 
individual is sleeping or concentrating on a specific task.)(4) Patients also 
experience Bradykinesia, which is the clinical term for slowness to initiate 
or complete movements.  This generally influences all actions, eventually 
even swallowing and blinking.  Muscular rigidity makes seemingly simple 
things like rolling over in bed extremely difficult or impossible.  In 
advanced Parkinson’s, a stooped appearance is assumed, due largely to the 
loss of exterior muscle tone.  The loss of this muscle also makes the limbs 
resistant to outward movement, sometimes resulting in contracted knees, 
elbows, and neck.  Reflexes are also hindered; patients will walk with small, 
careful steps, not swinging their arms.  Some patient’s experience loss of 
facial expression, drooling, the inability to speak clearly, loudly, or with 
a change in tone.  General aches and pains caused from stiffness, cramping, 
and falling down are also a problem, as is imbalance.
Autonomic systems including cardiovascular, urinary and digestive 
tracts may also be effected.  This is manifested in high blood pressure, 
urgency and frequency of urination, and a general slowness of the 
gastrointestinal system, including constipation.
Depression and dementia are also associated with Parkinson’s, although 
a concrete correlation has not been found.  It is estimated that 
approximately one third of individuals experience cognitive impairment.(5) 
Given that the age of the typical Parkinson’s victim is over 60, a degree of 
normal old age forgetting may cloud cognitive facilities (and the patient may 
be suffering from some other disease, such as Alzheimer’s.)  Some drugs used 
to treat Parkinson’s also cause confusion and lack of clarity.  About 40% of 
individuals develop depression, usually within the first year of the disease.  
Some think this may result from the dysfunction in neurotransmitter 
processing, some think it is an understandable response to the realization 
and endurance of such a difficult disease.(3)
Parkinson’s disease currently affects approximately one million 
Americans, second only to Alzheimers.  It has traditionally been seen as an 
idiopathic, non-genetic disease, but a recent study has found that a 
correlation does exist between twins.  Researches found a listing of 17,000 
twins listed in a World War II era registry and found that 161 pairs where at 
least one brother had Parkinson’s.  The results showed that there is a 
genetic link, but only in early-onset Parkinson’s (cases that begin earlier 
than fifty years old.) Only four pairs of identical twins and two sets of 
fraternal twins were found to both have the disorder.(6) Another study found 
that there might be an abnormal gene that is inherited, once again, only in 
early-onset Parkinson’s.  Out of eighty 1st degree relatives, 22.5% tested 
abnormally on motor function, sense of smell and mood, while only 9% of the 
control group did.(7) Mayo researchers recently discovered a chromosomal 
mutation in a 6th generation Iowa family (who have continuously been affected 
with Parkinson’s) that is helping solve the puzzle of it’s genetic path.  
Ultimately however, it remains nearly impossible to predict whom Parkinson’s 
will affect.(8)
If lack of dopamine is the only problem in Parkinson’s, why not simply 
supply the needed substance?  There is a barrier between bodily manufactured 
dopamine and dopamine made in the brain that functions as a neurotransmitter.  
The majority of an individual’s dopamine is made in the adrenal glands.  It 
is supplied to the bloodstream to work as a hormone, regulating blood 
circulation and heart rate.  If the mass quantity of dopamine produced 
peripherally were able to permeate the brain, a delicate balance would be 
upset.  To prevent this there is an impervious membrane that surrounds the 
brain neurons, called the blood brain barrier.  This is why dopamine given 
intravenously is not effective in treating Parkinson’s Disease.
Eventually scientists were able to find a building block, a chemical 
component which would be allowed entry into the brain and provide remaining 
nigral cells the needed parts to produce dopamine.  It is called 
levodihydroxyphenylalanine, thankfully abbreviated to levodopa, or L-dopa.  
When given to patients parkinsonism, (the collective features of the disease) 
reduces greatly.  Originally doctors assumed they had found a cure for 
Parkinson’s, but problems arose.  Only about 1% of the administered levodopa 
was absorbed in the brain.  The remaining converted dopamine remained in the 
body, causing heart palpitations and a racing pulse.  In some cases it led to 
a sustained twitching of the heart rather than an actual beating, and 
affected blood pressure resulting in faintness or blackouts.
Fortunately, a drug was found that stopped levodopa from converting 
into dopamine in the body, called carbipoda.  The combination of levodopa and 
carbipoda is put in pill form and marketed as Sinemet, (or various other 
brand names).  The drug is available in various ratios and tailored to each 
individual patient.  Other chemicals have been synthetically created to mimic 
dopamine, called dopaminergic drugs.  They are derived from a fungus called 
ergot, and are most effective when administered in conjunction to levodopa.  
Unfortunately, the beneficial effects of these drugs have been shown to only 
last a few months, and in some cases have been toxic to certain organs.(3) 
Though levodopa is currently the best and most effective treatment for 
PD, it has its own possibly quite serious side effects.(9) Dyskinesia, which 
refers to spastic, uncontrolled movement is common, as is the on/off 
phenomenon, where the person has control over their muscles one minute and 
the next does not.  Dyskinesia, (meaning dys “disorder” and kinesia “motion”) 
varies from periodic muscle contractions, to writhing limbs, to 
uncontrollable dance like movements.  This can cause fatigue, frustration, 
and embarrassment. Generally, the higher the dosage of levodopa, the more 
severe the dyskinesia. Generally, these episodes occur at the beginning or 
end of the levodopa distribution period (when the percentage of dopamine is 
at its lowest.)  Symptoms may also include impaired mental concentration and 
anxiety.(3)
A theory attempting to explain the “on-off phenomena” is when L-Dopa is 
ingested, remaining dopaminergic neurons lose the ability to store dopamine 
and develop a reliance on an exogenous supply.  The medicine has a wax and 
wane effect,(called pulsativity) which results in the fluctuation of motor 
control. Because of this, dopamine agnostics have been becoming more popular 
because they don’t have pulsativity, (or this stage is transient.) It is also 
thought possible that they may slow the progression of the disease by being 
neuroprotective.  COMT inhibitors, entacapone (Comtan) and tolcapone 
(Tasmar), are enzymes that brakes down levodopa, so when give concurrently, 
increases Central Nervous System delivery of dopamine.  It also provides a 
more controlled concentration of levodopa, decreasing pulsativity.  
Unfortunately, side effects to these drugs have included nausea, vomiting, 
and psychiatric disturbances. 
There are a plethora of drug treatments being given today.  
Dopamineagnostics, selegiline, anticholinergics, amantiadine, and most recently 
O-methyltransferase are in use.  Beyond drugs, innovative new techniques such as 
surgery and fetal tissue transplants are being explored.  Researches have found 
that if areas of the basal ganglia are destroyed, dyskinesias caused from 
levodopa therapy lessened.  Deep brain stimulation with microelectrodes in the 
thalamus has been shown to control tremors.(9) President Reagan banned fetal 
tissue research eleven years ago, but Clinton lifted the ban five years later.  
Limited research since then has involved researches removing substancia nigral 
cells from aborted fetuses and placing them in people with PD. Results are not 
entirely conclusive but scientists are optimistic.(10)
Science is constantly progressing in phenomenal new ways.  Very recently a 
group of researchers (cooperating with scientists at the Sahlgrenska Hospital in 
Sweden) in San Diego found that hippocampus brain cells can reproduce 
themselves.  This is a fascinating, ground breaking discovery that eradicates 
the traditional belief that neurons cannot regenerate.  Discoveries such as 
these provide helpful new insight into the working’s of the brain, which may 
lead to better understanding of Parkinson’s, as well as other enigmatic 
neurophysiological illnesses such as Tourette Syndrome and Huntington’s 
Disease.(11)
Physical therapy is an important part of dealing with all degenerative 
illnesses.  Muscle strengthening, stretching, and coordination practices help 
the patient physically and emotionally.  To asses the progress of their 
patients, therapists often use timed walking intervals, writing coordination, 
and common movement practices such as turning over in bed.(12) Sidney Dorros, 
who was the first patient to undergo experimental L-dopa treatment, recommends 
to people with Parkinson’s to learn as much about the disease as they can.  
Sometimes patients may be hesitant to learn because they fear it will be too 
depressing, but the opposite is usually true.  Another important component to 
actively coping with PD is to find the best doctor possible, not only one who is 
medically competent, but who has a genuine interest in the patient’s experience 
and narrative.(13)  For some patient’s, including family and friend’s in medical 
and perhaps therapeutic encounters can make things easier. Equally as important 
is keeping in mind that medical advances are being made, resulting in the 
symptoms and pathology of Parkinson’s becoming more tolerable. 
  			

Bibliography:
(1) Duvoisin, Roger C.  Parkinson’s Disease, A Guide For Patient and 
Family.
New York: Raven Press, 1978
(2) Martin, G. Neil.  Human Neuropsychology.
London:  Prentice Hall, 1998
(3)  McGoon, Dwight C.  The Parkinson’s Handbook.
New York: WW Norton & Company, 1990
(4)  Lechtenberg, Richard.  The Psychiatrist’s Guide to Diseases of the 
Nervous System.
New York: Wiley Medical, 1982
(5) Stolberg, Sheryl Gay.  “Reno Puts a Public Face on Often Private 
Disease.”
The New York Times  15 August 1999: p. 16
(6) “Twin Study Links Parkinson’s Disease to Environment.” 
The New York Times  2 Feb 1999: p. 12
(7) “Mayo Researchers Fit New Piece in Parkinson’s Puzzle.”
Medical Industry Today 21 Dec 1998
(8)“New Tests ID At Risk Relatives.”
American Healthline 11 March 1999
(9) Conley, Scott C., Kirchner, Jeffrey T.  Post Graduate Medicine
August 1999: p. 41
(10) Stolberg, Sheryl Gay.  “Decisive Moment on Parkinson’s Fetal 
Transplant.”
The New York Times  20 April 1999: p.2
(11) Holcomb, B. Noble.  “Adult Brain Cells said to Reproduce.”
New York Times 30 Oct 1998: p.1
(12) Guberman, Alan.  An Introduction to Clinical Neurology.
Boston:  Little, Brown, 1994
(13) Dorros, Sidney.  Parkinson’s, A Patient’s View.
Washington D.C.: Sevent Locks Press, 1981



Huntington’s Chorea
Paul Achuff

 In 1872, George Sumner Huntington presented before the Meigs and Mason 
Academy of Medicine a paper about a hereditary form of chorea (Knight, 1992). 
Although a hereditary disorder with presenting symptoms identical to what was 
illustrated before the Academy of Medicine was expressed thirty years prior, 
Huntington was the first to provide a clear and concise report regarding the 
chorea. With his report shortly becoming the standard description of the 
chorea, his name was quickly associated with the disease.
 As a child, George Huntington would accompany his general practitioner 
father as he made his rounds throughout Eastern Long Island. It was during 
these trips that George would encounter his first cases of chorea. His 
secluded early experiences with “Huntington’s” chorea lead him to believe 
that it was exclusive to the east end of Long Island (Knight, 1992). As he 
became more educated, this erroneous belief quickly dissipated. While the 
precise origin of Huntington’s chorea remains unidentified, Huntington was 
able to trace 1000 cases of the disease in twelve generations descendant from 
two brothers living in Suffolk, England during the 17th century (Huntington, 
1872). Irrespective of its origins, Huntington’s disease (HD) is now 
worldwide. The incidence rate has been estimated at 2 to 7 per 100,000 
persons (Martin, 1999) to 30 to 70 cases per million persons (Palo, et al., 
1987). 
 Huntington’s disease is now firmly established as a widespread hereditary 
disorder marked by both psychological and physical changes occurring later in 
life. This paper will first examine symptoms and consequences associated with 
HD before delving into the neuropathology and aetiology of the disease. 
Finally, treatment and presymptomatic testing will be discussed.
 Like Parkinson’s disease, HD has an insidious onset and is characterized by 
chorea and dementia. Greek for “dance”, chorea is most evocative of the 
manner such patients present (Martin, 1999). The persistent idiosyncratic 
patterns of involuntary flowing movements resemble the rhythmic flow of 
dance. The initial stages of the disease are marked by irregular and fitful 
action of the facial muscles and distal extremities. At this stage, the 
misdiagnosis of a tic disorder is not uncommon. Moreover, only 60 percent of 
patients are correctly diagnosed as having HD on their first admission to the 
hospital (Knight, 1992). The slight choreic movements during the first stages 
are easily voluntarily suppressed. Stereotyped movements include flexion of 
the trunk or of a knee, bobbing of the head, and flexion and extension of the 
fingers (Paulson, 1979). With the progression of the disease, however, the 
movement disorder becomes more generalized. As more muscle groups become 
involved movements become more obvious and occur with greater amplitude. As 
the disorder progresses and involves the trunk, a distinctive gait develops. 
Rigidity and dystonia predominate in the later stages of the disease. In the 
nearly terminal stage, patients may display pelvicural contraction, a fetal 
position of flexion with increased tone (Knight, 1992).        
 The symptoms seem to be intensified by stress. Moreover, the involuntary 
movements are absent during sleep and can be easily controlled by others 
without causing undue discomfort. Bradykinesia, while more characteristic of 
Parkinson’s, is also found in patients with HD (Knight, 1992).
  While fortunate individuals will manifest far more motor than mental 
problems, it is rare to discover a patient with marked motor difficulty who 
does not also manifest deficits in intellectual functioning. Indeed, slight 
personality and behavioral changes may antedate the motor difficulties by up 
to ten years (NINDS, 1998). In the five years subsequent from the genes 
expression the most pronounced deterioration involves verbal, spatial, 
arithmetic, and conceptual functions (Knight, 1992). However, the cognitive 
impairments associated with HD do not generally develop in a uniform matter. 
The inexorable progression of the disease soon results in dementia. In the 
early stages of the disease, the dementia is not a global, homogeneous 
decline in ability. Moreover, long term semantic memory and immediate recall 
often persist throughout the progression of the disease (Knight, 1992). 
 Psychiatric symptoms reflect the degeneration of limbic and cognitive 
circuits. Schizophrenic psychotic features such as delusions of grandeur, 
suspiciousness, and excitability are seen in many patients as a consequence. 
As the disease progresses to involve the prefrontal cortex, difficulties with 
problem solving, planning, organization, and selective attention result 
(Knight, 1992).
 Clinical reports suggest that dementia and psychosis are more common in 
Huntington’s than Parkinson’s disease (Lieberman, et al., 1979). Moreover, 
although not considered to be an aphasia, speech becomes difficult and 
dysarthic as the disease progresses. Although changes in the optic nerve are 
not observed, ocular movements may also be impaired. No obvious sensory 
deficits are seen in HD. Furthermore, patients with HD are often diagnosed 
with depression (NINDS, 1998). The depression most likely results from the 
progressive incapacitation and the inevitability of the disease. 
 In a retrospective study of 110 patients with HD, 39 per cent met the DSM 
criteria for depression, 9 per cent met the criteria for schizophrenia, and 
72 per cent displayed significant personality changes (Shiwach, 1994).  

 The transmission of HD is by autosomal dominant inheritance and is 
characterized by progressive and selective neural cell atrophy resulting in 
marked motor and cognitive deficits (Bradshaw, et al., 1998). Since it is an 
autosomal dominant disease, the defective gene needs only to be inherited 
from one parent. Each child of a HD parent has a 50/50 chance of inheriting 
the HD gene. If the gene is inherited, it will be expressed. Although genetic 
inheritance is the most likely cause of the disorder, it is possible for HD 
to occur without familial genetic predisposition. Sporadic HD is thought to 
be caused by a mutation of the gene during sperm development which results in 
CAG repeats (Knight, 1992), which will be discussed later. While a child can 
inherit the HD gene from either parent, sporadic HD is linked only to the 
father. 
 Although expression can occur from childhood into late life, the age of 
onset is generally around 40 to fifty years. The advancement of the disorder 
is relentless, usually causing death in 15 to 20 years after onset (Martin, 
1999). The disease progresses most rapidly in patients with juvenile onset 
HD, and death often follows in 10 years (NINDS, 1998).
 The disease has been genetically mapped to the tip of the short arm of 
chromosome four, 4p16.3 precisely (MacDonald, et al., 1992). Huntington 
disease is thought to result from the expansion of a trinucleotide (CAG) 
repeat located in the coding region of the gene for the protein huntingtin. 
An abnormal form of huntingtin is produced as a result of the repeated 
cytosine adenine guanine sequence. The presence of the abnormal huntingtin 
gene precedes HD. Some forms of familial Parkinson’s disease may also involve 
trinucleotide repetition (Knight, 1992). Individuals who do not have HD 
generally have 28 or fewer CAG repeats. Individuals with 40 or more repeats 
will theoretically develop HD (NINDS, 1998). 
  Postmortem examinations of HD patients reveal distinct atrophy of the 
striatum, particularly the head of the caudate nucleus, the anterior putamen, 
and the globus pallidus (Martin, 1999). However, a generalized cortical 
atrophy is also evident. Before death, neuronal atrophy of the striatum, 
particularly the caudate nuclei, is evidenced by the reduction of glucose 
metabolism within the cells. Atrophy of cortical layers 3,5, and 6 (Knight, 
1992) is particularly responsible for an up to 20 per cent reduction in brain 
size (Martin, 1999). 
 Although the specific cause of cell death in HD is as of yet unknown, one 
common theory subsists. Excitotoxicity is the over stimulation of cells by 
natural chemicals found in the brain. Glutamate and related acidic amino 
acids apparently destroy neurons by excessive stimulation of excitatory 
receptors located on the dendrosomal surfaces. The neuronal atrophy seen in 
HD can be induced in animals by administering an excitatory amino acid 
similar to glutamate, kainic acid. The strong excitatory effects of kainic 
acid excessively stimulate excitatory receptors resulting in neuronal 
depletion in the striatum. The excessive excitation of neurons produced by 
activation of specific receptors could result in neural degeneration in 
regions of the central nervous system where the amino acids accumulate 
(Olney, 1979). Furthermore, GABAergic and cholinergic striatal neurons are 
systematically altered as a result of the excessive stimulation. 
Consequently, the dopaminergic nigrostriatal fibers become uninhibited, 
resulting in the predomination of dopamine over acetylcholine. The elevated 
levels of the excitatory dopamine may possibly cause the choreic movements. 
Moreover, the overactivity of the dopaminergic system may be responsible for 
producing the schizophrenic features in HD.
 As mentioned, the efficacy of the cholinergic system in HD patients appears 
to be diminished. A decreased muscarinic receptor concentration and decreased 
values of cholineacetyl tranferase have been reported (Barbeau, 1979). 
Deficient levels of GABA have also been reported in patients with HD (Perry, 
et al., 1973). Low cerebral spinal fluid levels of GABA and decreased levels 
of cortical glutamic acid decarboxylase provide supporting evidence (Barbeau, 
1979). 

 While there is no available treatment to stop, delay, or reverse the course 
of the disease, pharmaceutical intervention may help keep clinical symptoms 
under control. Neuroleptics may help alleviate choreic movements and may help 
control schizophrenic features, apparently by regulating the dopaminergic 
system (Knight, 1992). SSRIs are generally prescribed to combat depression. 
Lithium may be prescribed to control lability and benzodiazepines may be used 
to alleviate anxiety (NINDS, 1998).
 The knowledge that HD is genetically inherited raises many personal ethical 
issues. Accompanying the discovery of the HD gene in 1983 was the ability and 
desire to perform presymptomatic testing. Since 97 to 99 per cent of HD is 
inherited (Knight, 1992), presymptomatic testing allows at risk individuals 
to determine whether they have the disease. For those diagnosed with HD, 
there are immediate problems with adjustment. Reactions range from “relief 
and calm to depression or despair” (NINDS, 1998). If the diagnosis is 
unexpected, suicide is common. Even if a person is unaffected, he must accept 
the stark realization that other family members probably possess the 
defective gene.
 Ethical dilemmas arise with the realization that HD can currently only be 
eradicated by the avoidance of reproduction. This is made more difficult by 
the late manifestation of the disease. The gene may be passed onto the next 
generation before the disease is realized. However, prenatal testing allows 
genetic material from a fetus to be analyzed. Since the probability of 
inheriting and not inheriting the disease is equal, predictive testing using 
fetal tissue can determine more precisely the risk factor. If the parent is 
completely opposed to abortion, this test should probably not be performed. 
Regardless, at risk individuals should seek genetic counseling prior to 
conception to alleviate any problems. Future advances in presymptomatic 
testing and in vitro fertilization may someday lead to the elimination of the 
disease.




Bibliography

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Bradshaw JL, et al. Motor sequencing problems in Parkinson’s disease, 
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Piek, ed. Human Kinetics:Champaign, IL, 1998, pp. 305 to 317  

Huntington G. On chorea. Med Surg Reporter 26:317 to 321, 1872

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Martin GN. Human Neuropsychology. Prentice Hall:London, 1999

MacDonald ME, et al. The Huntington’s disease candidate region exhibits many 
different haplotypes. Nature Genet 1:99 to 103, 1992

National Institute of Neurological Disorders and Stroke. 
19 Nov 98. http://www.ninds.nih.gov 

Olney JW. Excitotoxic amino acids and Huntington’s disease. . Advances in 
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Palo J, Somer H, Ikonen E, Karila L, Peltonen L. Low prevalence of 
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Paulson GW. Diagnosis of Huntington’s disease. Advances in Neurology Vol 23, 
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184

Perry TL, Hansen S, Lesk D, Kloster M. Amino acids in plasma, cerebrospinal 
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Shiwach R. Psychopathology in Huntington’s disease patients. Acta Psychiatry 
Scand 90:241 to 246, 1994  

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