There are two ways of looking at induction time. Since the exposure may need to accumulate to a certain threshold, other factors have to be present before the disease can occur. Accumulation takes a period of time termed 'the induction period.' Alternatively, the exposure may be the first event in a series of causal events that must occur for the disease to develop. For example, Susser Syndrome may be the result of a) a susceptible individual's accumulated exposure to a chemical, leading to b) a genetic damage which leads to c) a decrease of a certain neurotransmitter. This process may take months or years. Individual susceptibility varies based on specific biological/ physiological factors. (Giesecke, p.176-177)