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A case-control study of Parkinson's disease (PD) was conducted in the city …


Biology Articles » Genetics » Ecological Genetics » Genetics, drugs and environmental factors in parkinson's disease (A case-control study) » Methods

Methods
- Genetics, drugs and environmental factors in parkinson's disease (A case-control study)

The city of Rio de Janeiro has a population of approximately 5 000 000 inhabitants and is the capital city of the State of Rio de Janeiro. Between January 30, 1996 and February 1, 1997, subjects diagnosed with PD (n = 92) were randomly selected at the Neurology Department of IASERJ Central Hospital (Instituto de Assistência aos Servidores do Estado do Rio de Janeiro), located in the center of the city. Controls (n = 110) were selected in the same hospital and were matched to subjects according to sex and age (± 2 years). All controls underwent examination and those showing any parkinsonian or dementia signs were excluded. Distribution of diagnoses among control patients was: rheumatoid arthritis (1.2%), sciatica (11.9%), migraine headache (12.5%), tension headache (8.1%), dizziness (36%), polyneuropathy (26.1%) and myelopathy (4.2%).

All subjects were examined at least more than once by the same neurologist (ALW). Subjects with atypical features suggesting other forms of secondary parkinsonism, severe dementia or any history of cerebrovascular disease were excluded. Participants received a questionnaire (Chart 1) to be filled out during a face-to-face interview with the examiner. Questionnaire test-reliability was initially assessed with a small group of subjects (n = 5). Phase two took place 1 month later. No relevant variance between time points could be evidenced in all variables. The interviewer was not blind to respondent case versus control status, although the purpose of the study was not revealed to respondents. For PD diagnosis, criteria proposed by Calne et al.15 were used for a definitive diagnostic associated to stage 3 of the UKPDB16. For the ruling out of this diagnosis, step 2 of the UKPDB was used17.

Risk factors were investigated as follows: 1 ¾ Rural living prior to appearance of signs and symptoms: the individual had to have lived in this kind of environment for a period never inferior to 15 years; 2 ¾ Potable water-well source: for a minimum period of 15 years before appearance of symptoms. 3 - Inhaling and/or handling herbicides and/or pesticides: a minimum period of 15 years in contact with such substances was deemed necessary for entry. 4 - Cigarette smoking: as a protective factor, a minimum period of 8 years of consumption was required. If the individual reported that consumption had been suspended during the last 2 years prior to the onset of disease, this variable was taken into consideration. 5 - History of central or peripheral nervous system trauma: when central trauma was reported, besides its temporal relation to the individual, it had to have happened concurrently with important symptoms, like transitory consciousness loss or even headache and/or dizziness lasting for more than 2 days after the occurrence of trauma. 6 - Drugs with parkinsonian effects: to bear any relation to PD, the use of such drugs had to have lasted for a minimum period of one year, besides the fact that its use should have been suspended at least one year prior to the onset of the evolution symptoms of the disease. 7 - PD family history: subjects should report any relatives with the disease, with additional information on the evolution of symptoms for each individual. 8 - Inhaling or handling chemical agents with parkinsonian action: a minimum period of 15 years in contact with such substances was required.

The method consisted of an investigation through univariate, stratified and multivariate analyses. 1 - Univariate analysis: data obtained from evaluation of variables were examined as follows: a) X2 no parametric test (chi-square) indicated for the identification of tables that use crossed frequencies, aiming to examine the occurrence of associations among the factors. If any of the cells presented a frequency of less than 5, Fisher's exact test would then be used. b) Odds ratio related to frequency values, and also as a means to interpret the influence of some specific factors related to PD occurrence. Methodology applied took into account the significance level probability of 5% (p < 0.05). 2 - Stratified analysis: conducted to confirm variables that could provide significant statistical representation by confronting data obtained from these variables and also to assess to what extent one variable can influence the others. 3 - Multivariate analysis: its purpose was to avoid any bias resulting from combined effects among factors. This was effected based on a model of logistic regression, and individual analysis of parameters was used to complement data.

 


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