Guam

“Lytico,” a motor disorder with features similar to ALS, was first seen in the Chamorro people of Guam in 1904. An epidemic of Lytico occurred in the 1940s. Later in the epidemic, the clinical manifestations of the disease changed as “Bodig,” motor function similar to Parkinsonism, became the predominant form. Lytico-Bodig is also referred to as ALS/Parkinsonism dementia complex (ALS-PDC). At the epidemic’s peak in the 1950s, the prevalence, incidence, and death rate of ALS among the Chamorro on Guam were 50-100 times that of the worldwide average, with approximately 12 cases per year between 1940 and 1960 (2,3). The incidence of ALS in Guam varied by region, with four villages at the southern end of Guam having particularly high incidences of over 175 cases per 100,000 people at the the disease’s peak, over twice the highest incidence found in other regions on Guam (3). Since 1955, rates have greatly declined (2,4).

As no evidence of familial ALS was found, various hypotheses for the environmental causes of ALS in Guam pointed to various potential causes, including a slow virus, mineral imbalances in the water, exposure to heavy metals such as lead, and Chamorro customs, particularly that of using cycad seeds in traditional foods and medicines (3). Of these, the cycad hypothesis has gained the most ground. Cycad plants engage in symbiosis with cyanobacteria, which produce the neurotoxin BMAA which then becomes concentrated within the cycad seed. BMAA has been found to induce neuronal degeneration and impaired motor function in primates (2,4).

Cycas circinalis, the variety of cycad used by the Chamorro.

 

References:

  1. Ince, P.G., Codd, G.A. (2005). Return of the cycad hypothesis–does the amyotrophic lateral sclerosis/parkinsonism dementia complex (ALS/PDC) of Guam have new implications for global health? Neuropathology and Applied Neurobiology, 31, 345-353.
  2. Kurland, L. T. (1988). Amyotrophic lateral sclerosis and parkinson’s disease complex on Guam linked to an environmental neurotoxin. Trends in Neurosciences, 11(2), 51–54. http://doi.org/10.1016/0166-2236(88)90163-4
  3. Reed, D. M., & Brody, J. A. (1975). Amyotrophic lateral sclerosis and Parkinsonism dementia on Guam, 1945-1972. I. Descriptive epidemiology. American Journal of Epidemiology, 101(4), 287–301.
  4. Spencer, P. S. (1987). Guam ALS/parkinsonism-dementia: A long-latency neurotoxic disorder caused by “slow toxin(s)” in food? Canadian Journal of Neurological Sciences, 14(3 SUPPL.), 347–357.

Images:

  1. U. S. Government. (1991). English: Guam relief map. Retrieved from https://commons.wikimedia.org/wiki/File:Guam.gif
  2. Roi.dagobert. (2013). Français : Cône d’un pied mâle de Cycas circinalis dans la serre du Jardin des Plantes de Caen (Calvados). Retrieved from https://commons.wikimedia.org/wiki/File:Cycas_circinalis_m%C3%A2le_c%C3%B4ne.JPG