Huntington’s disease is genetic neurodegenerative disorder that is characterized by the presence of movement disorders, cognitive decline, and disturbances in behavior. (Gomez-Tortosa). A common trend in the research done on Huntington’s disease is the link between the juvenile, or early onset of the disease, and the adult onset of the disease. Differences in symptoms between these types is the defining distinction between the two; the juvenile form showing greater muscle problems, and the adult form showing greater levels of chorea, or movement problems.
An important issue to consider when interpreting or assessing any research study is validity. At the foundation of a sound review of a topic is the question asked by the study—a compelling question indicates initially, whether the researchers thought critically and creatively about their topic. This question must then be tested with rigorous techniques that ensure an objective, and therefore accurate analysis of the data collected. Lastly, sample size of the subjects tested must be taken into account.
Large sample sizes are favorable, but the sample size can be moderate if the rigor of the tests conducted is high. In the research paper, Dystonia-Predominant Adult-Onset Huntington Disease, the aim of the review conducted was to study the adult form of Huntington’s disease with respect to dystonia, or abnormal muscle contraction, a symptom predominantly present in the juvenile form of the disease. Chorea, abnormal involuntary movement, was noted as the predominant symptom of the adult-onset type. (Louis).
The goal of the study was to estimate the prevalence of cases of dystonia-predominant Huntington’s disease in a group of patients, and to study the relationship between the motor phenotype and the age of onset in the disease. This study expressed a high level of validity due to its willingness to test a large quantity of affected people, and its query into, and ability to make links between different age groups afflicted with Huntington’s disease. A strong aspect of this study was that it considered the manifestation of Huntington’s disease in young people in order analyze an adult form of the
disease. The aim was to look for the link between adult patients who showed Huntington’s symptoms present in juvenile patients—dystonia, specifically, which is atypical for the adult form of Huntington’s disease. The ability of the study to ask questions on age linkage indicates that the study thought critically about the characteristics of the disease. This key analysis of the subject combined with a significant number of patients used and tested with detailed techniques, suggests the authenticity of this review.
This study took a large sample size and therefore was able to assess a large number of patients. This sample size allowed for an increase in the validity of the research topic because it gave the researchers more data to investigate. 127 Huntington’s disease patients were given The Unified Huntington’s Disease Rating Scale or UHDRS. (Louis). This scale tested for specific symptoms of Huntington’s disease, such as chorea, rigidity, bradykinesia, eye movements, and most importantly, dystonia, the defining early-onset Huntington’s characteristic.
Every one of the considerable number of patients studied were given these series of tests, and then in turn received scores. The score from the dystonia test, the main juvenile symptom, was compared to the score from the chorea test, the main adult-onset symptom. The dystonia-predominant form of Huntington’s disease was identified by the severity of dystona relative to the severity of chorea. These strict methods of testing allowed for a clear analysis of the data from each patient, making this a reasonable study.
As in the previous study, Severity of Cognitive Impairment in Juvenile and Late-Onset Huntington Disease also explored the comparison between Juvenile and late-onset Huntington’s disease. While the previous study tested adult patients for the identification of a particular symptom common in juvenile cases, this study compared the cognitive functioning of three different age groups at the time of onset. This study was comprehensive in nature—taking into account and testing for several different afflictions that can affect an individual with Huntington’s disease, depending on age.
Assessments tested cognitive function through intense neuropsychological tests, and motor function through the Unified Huntington’s Disease Rating Scale. Ideas to consider were that patients with Juvenile onset of Huntington’s disease see a greater severity of symptoms, related to both neuropathological involvement, and the degree of functional disability. (Gomez-Tortosa). Genetically, juvenile patients also have longer CAG, trinucleotide repeats, when compared to the adult form. Genetic analysis, therefore, was also conducted on each subject to determine the number of CAG repeats present.
Though this study had fewer subjects than the previous article’s review, seventy one instead of 176, it was very detailed in the criteria for the subjects used, and very scrupulous in its tests. This suggests a high level of validity because each subject was able to be given greater attention in each evaluation. In this study, the seventy-one patients used were split into three very specific age groups: Juvenile onset, adult onset, and late onset. The parameters were very clear for each age group, juvenile being 25 years or younger, adult from 26-50 years, and late including 50 years or older.
These groups were then subjected to the tests to judge their cognitive and motor function. Cognitive function was measured through neuropsychological tests, encompassing aspects such as prefrontal, visuospacial, and memory functions. Motor function of each subject was measured through the Unified Huntington’s Disease Rating Scale, which is a 0-4 rating consisting of 0 being no motor impairment, and a 4 being the most severe motor impairment. (Gomez-Tortosa). Lastly, genetic analysis was conducted in order to test for the number of CAG repeats.
(See references chart for summary of tests conducted). This study’s precision in analysis of every listed symptom and aspect of Huntington’s disease made it very exact, which increases its reliability. It used the moderate amount of subjects it tested to its advantage, and left the least possible out when assessing each patient. In the study, Progression of Symptoms in the Early and Middle Stages of Huntington Disease, the aim was to investigate the symptoms present in both the early and middle stages of Huntington’s disease.
This study took a different approach to studying Huntington’s disease than the previous two because it asked family members of Huntington’s patients to observe and answer questions such as the patients’ disease progression, initial symptoms, and age at onset. The survey took 1238 individuals who had a family member with a minimum of a 6-year history of symptomatic Huntington’s disease. This study presented advantages over the other two in its sizable sample size, but lacked as a whole in its choice to gather information from people who were emotionally invested in each patient, such as family members. Objectivity, and therefore accuracy,
was lowered with this aspect of the testing. This study was meticulous in the structure of its surveys administered to participants, showing that this characteristic of the study was carefully thought out, and therefore reasonably reliable. The Affected Individual Questionnaire was requested to be completed by family members of patients. This questionnaire consisted of 19 physical, emotional, and cognitive signs commonly thought to occur during disease progression. (Kirkwood). The family members were also required to record information on demographics, disease progression, and clinical and psychiatric histories.
For every symptom the Huntington’s patient showed, the respondent was to answer at what time during the course of the disease it occurred: (1) within 1 year, (2) within 2 to 5 years, (3) within 6 to 10 years, (4) after more than 10 years, (5) has not occurred, or (6) “don’t know. ” (Kirkwood). The amount of information that was submitted on each Huntington’s patient was large and detailed. This presented a benefit to the study because it provided the researchers with a large amount of data on which to base their analysis, making this aspect of this study legitimate.
Though this study was able to gather a large amount of information, the tests conducted were not quite as detailed or as specific as those used in the previous two studies. This Progression of Symptoms study presented its main weakness in its choice of gathering information from family members of Huntington’s patients. The study was vast, analyzing a large number of participants, but the tests consisted of surveys—all of which were completed by the subjects, not the researchers. This method of testing allows for first-hand accounts and detailed information given by the subjects; however this information is subjective in nature.
These subjects have most likely watched their family member progress with the negative symptoms of the disease, and watched the everyday functioning of this loved one decline over time. An individual with a family member afflicted with Huntington’s disease might not want to believe that the symptoms present in that person are as severe as they are. A researcher running a study who conducts assessments does not have a personal connection to a Huntington’s disease patient; therefore, the information collected by a researcher is likely to be objective, and accurate.
This, in turn, would increase the reliability of the data collected. This study, however, did not take into account the subjectivity of the evaluation methods used. One last study, At Risk for Huntington Disease aimed to classify the clinical precursors which indicate the early onset of Huntington’s disease taking genes into account. The study was fair in its assessment by taking both men and women into the study and taking a large sample size to retain objective data, but lacked in the quantity of symptoms it was testing for.
This study categorized two classifications of clinical symptoms to assess: no specific motor abnormalities, and probable motor signs. A large sample size of 1001 adults at 50-50 risk for developing Huntington’s disease was used. The age group of the participants was 26 to 55 yeas due to that group being at the highest eligibility to develop Huntington’s disease. Blood samples were taken from each participant to measure CAGn of the HD gene, (Shoulson), with participants being assured that their personal data would not be revealed to any outside source.
Patients were also judged on their motor abilities. The genetic testing showed that there was a 2:1 ratio of women to men at risk for Huntington’s disease. The results showed that despite the gender difference of participants, the clinical characteristics of male and female participants were similar. In addition to this 92. 3% of participants were judged to have no or nonspecific motor abnormalities; and approximately 6. 7%, to have possible or probable motor signs. (Shoulson). This study was objective in its choice to gather a large sample size of both men and women, but lacked in its specificity.
It tested only for two different clinical characteristics of Huntington’s disease, either a manifestation of motor symptoms or not. It’s choice of genetic testing was sound, however, taking blood samples from participants and comparing the woman to man ratio of risk for the disorder. Huntington’s disease proves to be a complicated topic of study. With the many different types of symptoms and the varying levels of severity for each type of onset, there is room to conduct many possible combinations of studies.
In the current research presented, determining validity is a complete necessity. The first study discussed, the Dystonia-Predominant Adult-Onset review, showed positive points in a large sample size and critical analysis of an adult form of Huntington’s disease that showed early-onset characteristic. The fourth study, At Risk for Huntington Disease, also took a large sample size and retained an objectivity with sampling both men and women.
The third study, the Progression of Symptoms study took the largest sample size and planned out detailed tests, but fell short in its subjective method of testing; accuracy was compromised through the use of family members to conduct surveys, instead of objective researchers. The number of people sampled within a study is correlated with validity, but there are exceptions to this notion when methods of testing are taken into account. The second study discussed, the Severity of Cognitive Impairment study, proved that you could have an fair sample size but still conduct a very valid experiment with the assessment amount and meticulousness of the of testing processes.
Due to these characteristics, this study had the greatest legitimacy of the three reviews. Though these studies all varied in their legitimacy, their levels of validity were high. There is however room for improvement in the study of adult-onset and juvenile-onset Huntington’s disease. With the number of possible topics, there are many questions that can yet be asked and form the basis of future study. The most important part of a study is the critical query, and through analytical thinking, this is possible. [pic]
References Gomez-Tortosa E. , del Barrio A. , Garcia Ruiz P. J. , Sanchez Pernaute R., Benitez J. , Barroso A. , Jimenez J. F. and Garcia Yebenes J. (1998) Severity of Cognitive Impairment in Juvenile and Late-Onset Huntington Disease. Arch Neurol. , 55(6) : 835-843 Kirkwood S. C. , Su J. L. , Conneally M. , Foroud T. (2001) Progression of Symptoms in the Early and Middle Stages of Huntington Disease. Arch Neurol. , 58(2) : 273-278 Louis L. D. , Anderson K. E. , Moskowitz C. , Thorne, D. Z. , Marder K. (2000) Dystonia-Predominant Adult-Onset Huntington Disease. Arch Neurol, 57(2) : 1326-1330. Shoulson I. (2006) At Risk for Huntington Disease. Arch Neurol, 63(7) : 991-996.