Objective: To investigate the impact of environmental factors on eye movement performances in two populations composed of carefully selected healthy subjects with strikingly different ethnic origins and living in markedly different environments.

Background: In previous studies conducted in the French Caribbean islands of Guadeloupe and Martinique, we isolated specific parkinsonian syndromes, which are strongly believed to be caused by environmental toxins. These patients presented a dopa-resistant parkinsonian syndrome, with around half characterized by abnormal eye movement pattern when performing oculomotor tasks.

Methods: Eye movements were recorded in two groups, European subjects (n=63), long time residents of the Czech Republic, and Caribbean subjects (n=59), long-time residents of the French Caribbean. Both control groups performed the same oculomotor tasks, recorded with the same setup, acquired and analyzed with the same software. Caribbean subjects were specifically asked about their dietary exposure to annonacin, a toxin believed to cause atypical Caribbean Parkinsonism.

Results: Healthy European and Caribbean subjects differed markedly in their oculomotor behaviors, in both simple and more cognitive eye movement tasks. Compared to the Czech subjects, Caribbean subjects had slower maximum velocity of visually guided saccades, longer vertical saccade latencies, smaller vertical saccade gain and a higher frequency of square wave jerks. In the more cognitive antisaccade task, Caribbean subjects had longer latencies and higher error rates. Within the Caribbean group, high annonacin consumers had shorter visually guided saccade latencies and relatively lower vertical saccade velocities, two characteristics observed in patients at early stages of Progressive Supranuclear Palsy.

Conclusions: Our study revealed a specific pattern of oculomotor behavior observed in some of our Caribbean subjects that could correspond to a presymptomatic stage of atypical Parkinsonism, induced by toxic environmental factors. A follow-up study is warranted in the next years to confirm this hypothesis. In addition, beyond distinguishing between normal and pathological behaviors, this study emphasizes the variability of normative data across healthy populations and questions the appropriateness of control groups in clinical research.

References: Lannuzel A, Ruberg M, Michel PP. Atypical parkinsonism in the Caribbean island of Guadeloupe: Etiological role of the mitochondrial complex I inhibitor annonacin. Movement Disorders Vol. 23, No. 15, 2008, pp. 2122–2128. Lannuzel A, Edragas R, Lackmy A, Tressières B, Pelonde V, Edimo Nana Kaptué M, Mécharles S, Demas A, François B, McGovern E, Vidailhet M, Gaymard B, Roze E. Further evidence for a distinctive atypical degenerative parkinsonism in the Caribbean: A new cluster in the French West Indian Island of Martinique. J Neurol Sci. In Press.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/oculomotor-behavior-in-healthy-caribbean-does-it-reflect-an-increased-vulnerability-to-degenerative-parkinsonism/