Figure 2

Schematic representation of the cell loss kinetics predicted by a one-hit model. (A) Ratio of intact neurons (N(t)/N₀) as a function of time t shows an exponential decline in the one-hit model (Eq. 2 and 4). (B) When displayed on a semi-log graph, neuronal survival curves over time, producing a linear line. (C-E) PolyQ-length dependence of neuronal cell loss by the one-hit model. (C) Assuming that the extent of neuronal cell loss at the onset of disease is identical irrespective of polyQ-length (red line: 30% cell loss is defined as symptom onset), the relationship between polyQ-length and age of onset shows an exponential function (Eq. 6b), and then the time course of neuronal cell loss for each polyQ-length should be described by exponential kinetics, [as the disease proceeds, t(0.7) → t(0.3)]. (D) Relationship between polyQ-length and age at an identical ratio of cell loss for each repeat length shows an exponential shape. Red line: age at onset for each polyQ-length [30% neuronal loss, t(0.7)]. (E) Semi-log plots of polyQ-length versus age at an identical ratio of cell loss for each polyQ-length show that the slope (risks of cell death) are preserved during disease progression [t(0.7) → t(0.3)].