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Parkinson’s disease (PD) has long been considered as a prototype of a sporadic disorder with little or no involvement of genetic factors. Three to four decades ago, the typical perception of genetics in PD was that “it appears unlikely that heredity is an important determinant in the development of the disorder” . The discovery of SNCA mutations in 1997  started a new era of genetic studies in PD. We now know of at least 90 independent genome-wide association study (GWAS) risk variants in 78 loci that are associated with sporadic PD . Several other genes that are involved in familial, sporadic PD, or atypical forms of familial parkinsonism, have also been identified (Table 18.1).
To estimate the minimum prevalence of adult hereditary ataxias (HA) and spastic paraplegias (HSP) in Eastern Quebec and to evaluate the proportion of associated mutations in identified genes.
We conducted a descriptive cross-sectional study of patients who met clinical criteria for the diagnosis of HA (n = 241) and HSP (n = 115) in the East of the Quebec province between January 2007 and July 2019. The primary outcome was the prevalence per 100,000 persons with a 95% confidence interval (CI). The secondary outcome was the frequency of mutations identified by targeted next-generation sequencing (NGS) approach. Minimum carrier frequency for identified variants was calculated based on allele frequency values and the Hardy–Weinberg (HW) equation.
The minimum prevalence of HA in Eastern Quebec was estimated at 6.47/100 000 [95% CI; 6.44–6.51]; divided into 3.73/100 000 for autosomal recessive (AR) ataxias and 2.67/100 000 for autosomal dominant (AD) ataxias. The minimum prevalence of HSP was 4.17/100 000 [95% CI; 4.14–4.2]; with 2.05/100 000 for AD-HSP and 2.12/100 000 for AR-HSP. In total, 52.4% of patients had a confirmed genetic diagnosis. AR cerebellar ataxia type 1 (2.67/100 000) and AD spastic paraplegia SPG4 (1.18/100 000) were the most prevalent disorders identified. Mutations were identified in 23 genes and molecular alterations in 7 trinucleotides repeats expansion; the most common mutations were c.15705–12 A > G in SYNE1 and c.1529C > T (p.A510V) in SPG7.
We described the minimum prevalence of genetically defined adult HA and HSP in Eastern Quebec. This study provides a framework for international comparisons and service planning.
The age-at-onset (AAO) of Parkinson’s disease (PD) is thought to be influenced by environmental factors and polygenic predispositions. Professional exposures to pesticides and toxic metals were shown to be associated with an earlier onset in small sample studies.
Aim of Study:
The aim of this study was to confirm the association between professional exposures to pesticides and toxic metals and the AAO of PD, on a larger cohort of patients, defined with a clinic-based ascertainment scheme.
We used an incident cohort of 290 patients recruited through three designated movement disorder clinics in the province of Quebec, Canada. Patients completed a detailed questionnaire regarding professional exposures to pesticides and toxic metals. We compared the AAO in patients without prior professional exposure (N = 170) and those with exposure to pesticides (N = 53) or toxic metals through welding (N = 30). We further subdivided patients exposed to pesticides according to the frequency and proximity of their contacts.
Patients with prior exposure to pesticides (AAO = 54.74 years) or toxic metals (54.27 years) had a significantly earlier AAO compared to the control group (59.26 years) (p = 0.003). In those exposed to pesticides, closer (p = 0.03) and more frequent (p = 0.02) contacts were negatively correlated with AAO.
Exposure to pesticides and toxic metals were both associated with an earlier onset of PD, an effect that was greater with higher levels of exposure, both in terms of frequency and proximity.
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