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This paper, written by seventeen year old Adam Michaelson, has been entered into the Intel Science Talent Search in the USA, and we are, with Adam's permission, reproducing it here. Read on!

 

Behavioral and Attitudinal Effects of

Youth and General Onset

Parkinsonís Disease

By

 

Adam D. Michaelson

 

Oceanside High School, Oceanside, New York

 

 

RESEARCH REPORT FOR THE

INTEL SCIENCE TALENT SEARCH

(2001-2002 school year)

 

Summary

 

A sample of 78 people with Parkinsonís Disease was analyzed to examine effects

in their daily lives.† The data was collected through questionnaires distributed in the USA and Ireland.† The main findings demonstrate that there is a fine distinction between Youth Onset Parkinsonís Disease, or diagnosis before fifty years of age, and General Onset Parkinsonís Disease, or diagnosis after fifty years of age.† The data shows that people with Youth Onset Parkinsonís Disease experience a faster progression of the disease, more severe psychological effects, and a tendency toward rejection of medications. Because of the information collected, health care providers will learn how better to treat both types of Parkinsonís Disease and how to optimize patientís quality of life.

 

Introduction

†††††††††

Parkinsonís Disease affects more people than do Multiple Sclerosis and Muscular Dystrophy.† It strikes with no warning signs and at any age.† This disease is much different from Alzheimerís in that the sufferer is fully aware of the progression of the disease and all the disabilities that come with it.†

 

††††††††† The disease is classified as a neuromuscular disorder resulting from the degeneration of pigmented neurons in two areas of the brain: the substantia nigra and the locus ceruleus.† The disease is detected by the presence of Lewy bodies in these regions.† Lewy bodies are only present when pigmented neurons are dying or dead. There are many types of rarely occurring Parkinson Diseases that will not be examined in this study in order to discuss the effects of the disease on the majority of the population with the disease.† The following variations of Parkinsonís Disease will be excluded from this study: Vascular Parkinsonism or Parkinsonian symptoms resulting from a lack of oxygen and stroke, Infectious Parkinsonism or virus induced Parkinsonís Disease (like encephalitis lethargica), Drug-Induced Parkinsonism or symptoms resulting from persistent use of early tranquilizers like resperine, haloperidol, and chlorpromazine, and any of the diseases classified as Parkinsonís Syndrome (including chemical poison induced Parkinsonism and Pugilistic Parkinsonism) (Lieberman and Williams 1993). This study will only deal with the most common form of Parkinsonís Disease: Idiopathic Parkinsonís Disease. The remainder of this study will refer to Idiopathic Parkinsonís Disease as Parkinsonís Disease.

 

††††††††† This research is geared toward the dissection of Parkinsonís Disease. It will be compared to the same disease in another country, its effect on the quality of life of the sufferer, and the difference age of onset has on the disease.† The study relates certain aspects of the disease such as psychological effects, sleep disturbances, cognitive degeneration, rate of progression, contributing factors, quality of life, and medicinal side effects.

 

Since the study only examines the effects of the disease and not the physical degeneration of the dopamine in the brain, progression does not describe the disease in its natural state, but describes how the medicine and the disease progress together (Furukawa, Mizuno, and Narabayasi).† Also, progression of the disease is classified by symptoms and not by the decline in F-dopamine uptake in the brainís striatal subregion because of the recent study done at the University of Turku (Nurmi et al. 2001.

 

††††††††††† With the sustained efforts of scientists using stem cells, an end to Parkinsonís Disease looks promising.† However, until conclusive biological findings are made, social scientists must find out how to help the psyche of the Parkinsonís Disease patient.† If used correctly, the information attained from this study can increase the quality of life of patients. Certain distinctions will be made between Youth Onset Parkinsonís Disease (YOPD) and General Onset Parkinsonís Disease throughout the research. These distinctions may become instrumental in the medical as well as holistic treatment of each disease.

 

Literature Review

†††††††††

An intensive literature review was conducted in order to determine what information is available to both the Parkinsonís Disease patient and the researcher. Medical journals, Internet forums, and health care pamphlets were most useful throughout this study. It has been very important to understand the studies conducted by other researchers.

 

Quality of Life

 

In order to prove that Youth Onset Parkinsonís Disease and General Onset Parkinsonís Disease are different, the statistics must show that each disease affects the patient in a different way.† Without using any biological changes in the body for justification, the optimal mode of achieving this goal is through comparing the quality of life of each group of respondents.† An overall hypothesis must be drawn that states that one condition of the disease brings about a lower quality of life than another.† Quality of life is not a measurable variable.† However, Schrag, Jahuppshahi, and Quinn have stated that depression, disability, disease severity, and cognitive impairment account for the poorer quality of life in PD sufferers.† Upon analyzing this studyís data and interviewing Parkinsonís Disease patients, many psychological illnesses appear to accompany the disease. A fifth component appears necessary to compare the two groups.† This fifth component tests the psychological effects the disease has on the respondent.† These effects include anxiety, paranoia, agoraphobia, and hallucination.† In order to quantify the collected data, several individual indices have been created.† Only physical disability will be tested so as not to double count data.†

 

The five components thus are Disease Severity, Degree of Depression, Physical Disability, Cognitive Impairment, and Psychological Effects.† These five components are based on a zero to one scale where zero is most affected by the component and one is least affected by the component.† The sum of the five components represents the Quality of Life Index.† This can range from zero to five, where minimum quality of life is zero and maximum quality of life is five.† Each component has been evaluated independently as well.

 

Another indicator of the difference between YOPD and General Onset Parkinsonís Disease is found in the different of levelsof independence that the respondents feel.† An index was created to establish the degree to which the two subgroups were dependent upon a caregiver or relative where zero is independent and five is totally dependent. This test is useful in describing the difference in a change in lifestyle of respondents in each group.

 

Limitations

†††††††††

The questionnaire was limited to general issues of physical symptoms and observances rather than beliefs. Since General Onset Parkinsonís Disease is limited to geriatrics, it is difficult to discern between the effects of aging and the effects of the disease.† For future comparisons between Youth Onset Parkinsonís Disease and General Onset Parkinsonís Disease, a control group must be used for the measurement of cognitive impairment. According to all the information accessible, no previous studies have been done to compare YOPD to General Onset Parkinsonís Disease holistically.† Because of this, the statistics and analysis of much of the data in this study cannot be compared to other studies with the same hypotheses.† Also, the distribution of respondents across the Hoehn and Yahr Scale is not even.† Because Stage IV and Stage V patients experience a lack of motility and cognitive reasoning, answering a questionnaire is very difficult.† Thus, fewer questionnaires were received from this group than any other.† For future studies, an equal number of respondents from each stage should be important in comparing these stages.

 

Hypotheses

 

Based on the information acquired from interviews with patients, talks with Movement Disorder Specialists and current research in Parkinsonís Disease, the following hypotheses have been proposed for analysis.

 

1)     For the two-tailed test, the following comparisons were made:

 

        H0 There is no significant difference between the mean rate of progression of Parkinsonís Disease patients from the United States and Parkinsonís Disease patients from Ireland.

H1The mean rate of progression is greater in Ireland than in the United States.

 

        H0 The frequency of YOPD respondents and General Onset Parkinsonís Disease respondents experiencing denial of the diseaseís severity is equal.

H1 The frequency of YOPD respondents experiencing denial is greater than the frequency of General Onset Parkinsonís Disease respondents.

 

        H0 The mean Quality of Life Index is the same in YOPD and General Onset Parkinsonís Disease respondents.

†††† H1 The mean Quality of Life Index is higher in General Onset Parkinsonís Disease

respondents than in YOPD respondents.

 

Methodology

†††††††††

The main research tool used in this study was a questionnaire.† Two preliminary studies were conducted for the efficacy of the questions before the final version was produced.† Contacts were provided through support groups both online and in person.† Questionnaires sent to Ireland were distributed by a support group leader and then returned by mail.† The patients were asked neither their names nor geographic locations (excluding country) in order to ensure anonymity.† Most questionnaires were sent with cover letters with self addressed-stamped envelopes.† About fifteen of the questionnaires were sent via e-mail to only people who requested it and were members of the support group forum.† Upon return, the envelopes were discarded and each questionnaire was assigned a sequential number.

 

††††††††† The questionnaire was designed to investigate certain aspects of the disease. It asked for both subjective and objective answers.† Most questions were multiple choice with room for explanation and ďotherĒ answers where applicable.†

 

The makeup of the questionnaire was not based on any previously distributed questionnaires.† Respondents were unaware of the researcherís intentions to find distinctions in the onset of the disease.† Without this bias, many of the answers respondents gave were consistent.† Many previous studies have investigated differences in onset of Parkinsonís Disease to various factors of the disease.† But, despite intensive research, no previous study has tried to differentiate the two diseases as distinct.

 

††††††††† The data was analyzed with a TI-83 plus calculator and Microsoft Excel.† Descriptive statistics was used to show differences in mean, standard deviation, and frequency distribution.† For inferences, the two-tailed independent sample t-test and a two-sample t test statistic were used to evaluate the hypotheses.

 

Results

 

One hundred questionnaires were distributed with an unusually high response rate (84%) of 84 questionnaires returned.† Five surveys were disqualified from statistical analysis because they lacked answers to questions that were necessary in correlating data.† One survey was also disqualified since the respondent simultaneously was a part of a New York University drug study.† In effect, his answers to the questionnaire would be inaccurate whether he used his present conditions from the unknown drug or inconclusive because of uncertainty about symptoms before the study.† As a result, seventy-eight cases were available for statistical analysis.

 

The sample population was drawn from the United States and Ireland.† The respondents came from random parts of both countries to further ensure anonymity and geographic predisposition.†

 

The differences between the rates of progression for the subgroups of American respondents and Irish respondents were tested with the independent sample two-tailed t-test.† The two-tailed test with an acceptance level of .05 was selected because the direction of the correlation was not known.† As a result, the null hypothesis for rates of progression of both subgroups was accepted, because there was no significant difference found in the rates of progression.† Therefore, the rate of progression of Parkinsonís Disease is not affected by geographic location.† This test suggests that the American respondents and Irish respondents come from the same population of people with Parkinsonís Disease and will be used as such for the remainder of the study.

 

The sample consists of 34 respondents with onset equal to or younger than 50 (or YOPD respondents) and 44 respondents with onset greater than 50 (or General Onset Parkinsonís Disease respondents).† The most useful explicit information that respondents offered is the respondentsí rating on the Hoehn and Yahr Scale.

 

Table 1. The Hoehn and Yahr Scale

Stage I:

Symptoms are found only on one side of the body.

Stage II:

Symptoms are found on both sides of the body; walking and posture are affected.

Stage III:

The ability to walk is impaired and there is slowing of body movements.

Stage IV:

Severe symptoms include marked impairment in walking.

Stage V:

Complete immobility

(Schrag, Jahuppshahi, and Quinn 2000)

 

The respondents were distributed among the five stages as shown below.

 

Table 2. Youth Onset Parkinsonís Disease Respondents and General Onset Parkinsonís Disease

†††††††††††† Respondents By Hoehn and Yahr Stage


†††††††††††††† †††

 

The distribution of the respondents is indicative of the population of people with Parkinsonís Disease that can successfully write or dictate answers to the questionnaire.† As the disease becomes more advanced, the ability to perform normal tasks is hindered.† This includes filling out a questionnaire.

Upon understanding the stage distribution of the respondents, many factors become apparent. The sleeping habits in YOPD respondents and General Onset PD respondents are affected by stage.† While 100% of YOPD respondents beyond Stage I experience some form of sleeping disorder, only 63% of General Onset Parkinsonís respondents beyond Stage I recorded sleeping problems.† Poor sleeping habits and sleeping disorders can be attributed to either the disease itself or medications that treat the disease. No conclusion can be drawn from the questionnaires stating which reason is correct.† Since one or both of the attributions would cause the difference in respondents with sleeping orders, two observations can be made. Between the two groups, either the disease itself is different or the same medication affects the two groups differently.† Regardless of which hypothesis is true, either one indicates a marked disparity between the two diseases.

 

Another observation also became apparent when the two groups were split up into Hoehn and Yahr Stages.† Several times throughout the questionnaire respondents were given the opportunity to further support or contradict previous answers.† The most apparent and frequent contradictions came when General Onset Parkinsonís Disease patients beyond Stage II were asked about their independence.† Fourteen of the thirty General Onset respondents beyond Stage II described themselves as being ďcompletely independent, so much that (they) can live alone.Ē† Of those fourteen patients, ten responded that they are dependent on a caregiver or family member for much of their daily activities.† Only three of the thirty-four YOPD respondents answered in the same manner.† This inconsistency came as a surprise.

 

A two-tailed independent sample t-test with a 95% confidence level was used to evaluate the second hypothesis. A critical value of Ī2.145 was used.† The t value wasĖ2.460 and thus the H≠≠0 was rejected and the negation of the H1 was accepted. This test shows that less than 5% of all samples will show a smaller discrepancy in dependence on others.† It can be concluded that General Onset Parkinsonís Disease patients suffer from denial and problems with self-identity more so than the YOPD patient.

 

The Hoehn and Yahr Scale shows a difference in the average degree of dependence the respondents have on caregivers or family members as well. This index varies from zero to five.† Zero indicates independence while a maximum score of five shows total dependence.

 

Table 3. Average Dependence On Other Index In YOPD and General Onset PD:

††††††††††† Respondents Versus Hoehn and Yahr Stage


††

 


The above table indicates that geriatrics in general serves as a harbinger for dependence on others within a household.† Old age requires assistance without Parkinsonís Disease and thus the General Onset respondentsí dependence on others is skewed by the necessity for age based help.† It should be noted that even in the few years following YOPD diagnosis or in the first two stages, dependence on others is above zero. This means that men and women in their early 30ís and 40ís need assistance with caring for themselves.† Upon realizing that middle-aged respondents are unable to live without assistance, their overall quality of life was scrutinized.†

The following table compares the different components of the Quality of Life Index. †

 

Table 4. Comparison of the Means of Quality of Life in YOPD Respondents and General Onset PD††

†††††††††††† Respondents

 

Quality of Life Components

In YOPD Respondents

Mean

(Standard Deviation)

 

In General Onset

Respondents

Mean

(Standard Deviation)

 

Population Mean

(Population Standard Deviation)

Disease Severity

0.596

(0.320)

0.574

(0.283)

0.585

(0.298)

Degree of Depression

0.676

(0.475)

0.648

(0.401)

0.662

(0.433)

Disability

0.301

(0.406)

0.330

(0.377)

0.312

(0.386)

Cognitive Impairment

0.259

(0.310)

0.282

(0.372)

0.271

(0.344)

Psychological Effects

0.288

(0.346)

0.449

(0.394)

0.369

(0.370)

Quality of Life Index

2.120

(0.397)

2.283

(0.380)

2.202

(0.385)

 

†††††††††††

The table indicates an overall lower quality of life in YOPD respondents. Note that the population means and standard deviations are not known.† Because of this, a two-sample t test statistic is performed and yields a critical value of 1.8318.† When an estimate of 35 is used as the degrees of freedom, P lies between 0.05 and 0.025.† The data strongly supports the thesis that General Onset PD patients have a higher Quality of Life Index than YOPD patients.† A 95% confidence interval for the mean difference between YOPD respondents and General Onset Parkinsonís Disease respondents uses the critical value t*=2.030 of the t(35) distribution.† The interval is 0.163Ī0.181 which indicates that the General Onset Parkinsonís Disease respondents mean Quality of Life Index is anywhere from -0.019 to 0.345 higher than the YOPD respondentsí mean.† This data indicates that roughly 90% of all tests will yield a higherQuality of Life Index in General Onset PD respondents.† Although the analysis does not solidify the difference between the two diseases, it does indicate an unmistakable difference that requires further questioning and investigation.

 

The breakdown of the means must be analyzed while taking into account subjective shortcomings.† The statistics indicate that YOPD patients have an overall lower quality of life than [that of] General Onset Parkinsonís Disease patients.† It should be noted that Disease Severity Index is based solely on the point of progression of the disease. If a perfect sample size were taken, the Disease Severity Index between both groups would be almost identical and YOPD respondents would have a comparatively lower mark overall.† This, factored in with a certain coefficient of geriatric effect on Parkinsonís Disease would more evenly equate the two groups statistically.

 

The Quality of Life Index also demonstrates that YOPD respondents suffer more from psychological effects, disability, and cognitive impairment than General Onset respondents.† The increased suffering from disability and cognitive impairment suggest that YOPD and General Onset PD are different. The most common disability listed among YOPD respondents was the need for speech therapy. In General Onset PD respondents, a cane was sited as the most commonly needed aide.† Assuming that the two diseases are in fact different, this sample indicates that the loss of voice and speech patterns is more typical of YOPD than General Onset PD.† Cognitive Impairment was tested by asking questions about problem solving, word retrieval, and short-term memory loss.†

 

One of the most common signs of advanced aging is cognitive impairment.† For people over 50 years of age, cognitive impairment occurs naturally.† This further illustrates the difference in YOPD patients and General Onset Parkinsonís Disease patients.† Since cognitive impairment is aggravated by geriatrics, General Onset PD patients should have an overall lower Quality of Life component.† However, YOPD patients are shown as being more heavily affected by cognitive impairment.†

 

The differences in the two groupsí lifestyles must also be noted.† While YOPD respondents show busy committed lives, General Onset Parkinsonís Patients have much less to worry about.† Because stress and fatigue aggravate the symptoms of Parkinsonís Disease, the YOPD patient normally suffers worse from his own lifestyle than from the disease. The responsibility of the YOPD patient that comes with child rearing and providing for a family brings about psychological issues more often.† In this study, YOPD respondents indicate a much higher frequency and more severe nature of mental illness.† It is necessary to note that the lifestyle of a YOPD patient must be calmed after diagnosis.† In this way, psychological illnesses, faster disease progression, and disability can be avoided.

 

The intention of this research is to observe the behaviors and attitudes of both people with Parkinsonís Disease and persons in the medical profession as well.† An analysis of the questionnaires has shown a number of new significant findings that should be used to address the attitudes of persons specializing in movement disorders.†

 

The most interesting of the observations came while analyzing the Aggravating Factors portion of the questionnaire.† In a study from Neurology, pesticide exposure, family history of Parkinsonís Disease, and a history of depression were sited as predictors for Parkinsonís Disease. Exposure to pesticides and a rural living environment were considered the two major causes of Parkinsonís Disease.† The distinction in the two sets is that ďpredictorsĒ indicate pre-Parkinsonian conditions that are indicated after Parkinsonís Disease is diagnosed, while ďcausesĒ show conditions that have been scientifically proven to contribute to the development of Parkinsonís Disease (Hubble et al. 1993). Much of the data obtained from this study suggests different predictors for Parkinsonís Disease.†

 

Of the seventy-eight respondents, nineteen (nine YOPD and ten General Onset PD) reported some sort of brain injury before diagnosis.† In 1996, an independent study found that approximately 2 million brain injuries. including non-reported incidents. occurred in the US (Pallone 1996).† Of the 275 million people in the US, brain injuries occur at about a rate of 0.72% of the population.† In the YOPD sample size, 26.4% of the respondents reported some sort of brain injury before diagnosis.† Of the General Onset PD sample, 22.7% of the respondents noted brain injury.† The frequency of brain injury from this sample is not coincidentally high, but it is significantly high.† This suggests a link between head trauma and the development of Parkinsonís Disease.† Further studies should be performed in order to specify the exact reason for such a high occurrence.

 

Only two of the 78 respondents were chronic cigarette users prior to diagnosis.† As compared to the national average of 26%, a meager 2.5% of the sample of people with Parkinsonís Disease have smoked (Wellner 2001).† Surprisingly, this evidence seems unrealistic.† However, a Cohort study done in a Californian retirement community showed that risk of PD is significantly reduced by smoking, hypertension, coffee drinking, and alcohol consumption.† The statistics in the present study qualify the Cohort study in a random sampling from across the country.

 

It has been generally accepted that rural well water and prolonged pesticide exposure contribute to the development of Parkinsonís Disease.† But, of the 78 respondents, 70 reported living in an urban environment for at least 16 years.† A startling 89% of the sample size has been exposed to urban air pollution, drinking water, and stress for at least a quarter of their lives.† This generally contradicts the findings in the Hubble, et al. study.† Further investigation must be made in order to justify these results.

 

When asked which medications bring about the most side effects, YOPD respondents mentioned Sinemet as the medication.† Sinemet is a dopaminergic and is used to replace or mimic the actions of dopamine (Johnson 1995). These YOPD respondents regularly listed side effects of Sinemet that included light-headedness and fainting.† These side effects are normally only attributed to dopamine agonists, and not Sinemet.† From this observation, it should be noted that YOPD respondents experience side effects from the most common Parkinsonís Disease medication that people with Parkinsonís above the age of 50 do not.

 

Conclusion

†††††††††

The intentions of this study are to examine the human problems that patients have with Parkinsonís Disease.† People with Parkinsonís Disease are generally unsure of what effects the disease actually has on their lives.† Also, the PD sufferer cannot make distinctions between a medicationís shortcomings and the diseaseís severity.† In an effort to sort out many of these overlapping effects, this study has presented several viewpoints for treatment.† Because of this different perspective, subsequent studies should be performed in order to validate these findings.† Subsequent research should be tested with a larger sample size and a more concrete control group.†

 

When comparing the diseaseís effect on a patientís quality of life, a holistic approach is necessary.† The findings have underscored psychological effects, disability, and cognitive impairment as the strongest factors in lowering quality of life.† Compared to the other factors taken into consideration in this study, these three appear to be the most severe and life-altering effects of the disease.† Since the YOPD patient scores lower on the Quality of Life Index and suffers worse from these three factors, the disease affects YOPD patients more severely.†

 

Due to the disease, respondents have reported awkwardness with their spouse, inability to maintain a household, and an overall feeling of helplessness. It can also be concluded that General Onset Parkinsonís Disease patients suffer from denial and problems with self-identity more so than the YOPD patient.† But, if YOPD patients are affected more drastically in the way they think and act, then they are suffering from this disease more severely.† If Parkinsonís Disease changes the behavior and lifestyle of younger patients so drastically as to make them doubt their importance in a family, the younger patients have responded more severely to the disease.†

 

Because the impact Parkinsonís Disease has on YOPD patients is different from that of General Onset Parkinsonís Disease patients, the groups must be suffering from two distinct diseases.† If physiologically the diseases are proven to be the same, then its psychological impact on the two groups is indeed different.

 

Works Cited

 

Furukawa, Yoshiaki, Yoshikuni Mizuno, and Hirotaro Narabayasi. ďEarly-Onset Parkinsonism with Dystonia: Clinical Differences from Hereditary Progressive Dystonia or Dopa-Responsive Dystonia.Ē Advances in Neurology. 39:327.

 

Goldfinger M.D., Stephen E. ďA Special Report: Parkinsonís Disease.Ē† Harvard Medical School Health Publications Group.† Boston: President and Fellows of Harvard College, 1998.

 

Hietanen, Marja, and Heikk Teraevaeinen. ďThe Effects of Age of Disease Onset on Neuropsychological Performance in Parkinsonís Disease.Ē Journal of Neurology, Neurosurgery, and Psychiatry. 51(2) 2/1988: 244-249.

 

Hubble, Jean P., et al.† ďRisk Factors for Parkinsonís Disease.Ē Neurology. 43(9) (9/1993):1693-1697.

 

Johnson, Arlette.Young Parkinsonís Handbook. APDA, 1995.

 

Kostic, Vladimir S., et al.† ďEffects of Age at Onset on Frequency of Depression in Parkinsonís Disease.Ē† Journal of Neurology, Neurosurgery, and Psychiatry. 57(6) (10/1994): 1265-1267.

 

Lieberman, Abraham N. and Frank L Williams. Parkinsonís Disease.† New York: Simon and Schuster, 1993.

 

Michaelson, Adam D. (2000-2001).† [Interviews with Sydelle Lehrer and John Arnt].

 

Moskovitz, Charlene, et al. ďLevadopa Induced Psychosis: A Kindling Phenomenon.Ē† American† Journal of Psychiatry. 135(6) (6/1978): 669-675.

 

Nachmias, Chava and David.Research Methods in the Social Sciences.† New York: St. Martinís Press, 1992.

 

Nurmi, E, et al. ďRate of Progression in Parkinsonís Disease.Ē Journal of the Movement Disorder† Society.† 16(4) (7/2001): 608-615.

 

Paganini-Hill, Annlia.† ďRisk Factors for Parkinsonís Disease: The Leisure World Cohort Study.Ē Neuroepidemiology. 20(2) (2001): 118-124.

 

Pallone, Frank Jr. ďProviding Expanded Studies and Innovative Programs for Traumatic Brain Injury.Ē Congressional Record. Daily Edition. 142(100) (9 July 1996): H7126-7128.

 

Schrag, A., M. Jahuppshahi, and N Quinn.† ďWhat Contributes to Quality of Life in Patients with Parkinsonís Disease?Ē Journal of Neurology, Neurosurgery, and Psychiatry. 69(9) (2000): 308-312.

 

Snyder, Solomon H., and Robert J. DíAmato.† ďPredicting Parkinsonís Disease.Ē† Nature. 317(6034) (9/1985): 198-199.

 

Wellner, Alison Stein. ďBlowiní Smoke.Ē† American Demographics. 23(2) (2/2001): 20-21.