Is sporadic Alzheimer's disease associated with diphtheria toxin?

The two major aspects of Alzheimer's disease (AD) that must be considered in a search for causative agents are its association with aging and its widespread epidemiology. While a number of agents have been identified, additional factors may play a role. An association with diphtheria toxin was suggested by observations that vaccinations may provide protective effects, and the observation that decreased proteins synthesis in cortical regions from AD patients is associated with modification of elongation factor 2, the target of diphtheria toxin. While protection against diphtheria toxin is provided by vaccination, the known decline in the immune system associated with aging would result in a renewed sensitivity to the toxin. An association with diphtheria toxin would be consistent with the observations that the bacteria associated with the toxin, Corynebacterium diphtheria, is often found in the nasopharynx and an early symptom of AD is the loss of smell with a disease progression from the entorhinal cortex to the hippocampus and the neocortical areas. If diphtheria toxin is involved in sporadic AD, booster vaccinations given to elderly individuals might result in a decreased incidence of this disease. As booster DPT vaccinations are already recommended for individuals over 65, cognitive testing at the time of the booster and 5 years later, along with similar cognitive testing in age-matched individuals who decline vaccination, might provide an inexpensive method to investigate whether diphtheria toxin plays a role in AD and the efficacy of DPT booster vaccines for AD.