Figure 4
Correlation between polyQ-length and age of onset in patients with SCA3. A total of 308 patients with expanded CAG repeats in the ataxin-3 gene were analyzed. (A) Linear regression analysis using Eq. 19 with natural log-transformed [q – Ln(tA)] data against polyQ size provided the best fit to a linear model (0.0948x – 7.3787) when q = 4.29. The q value was determined by identifying the points at which the R2 were identical for a quadratic curve (red line) and a linear model (black line). (B) Residual analysis of standardized residuals versus standardized predicted values in the regression model of Figure 4A showed that the residual distribution was normal (i.e., mean = 0). Furthermore, the scattered points showed no clear pattern, suggesting that variance was constant. (C) Comparison of the regression model obtained from Figure 4A (pink line) to a linear regression of natural log-transformed tA versus polyQ-length (black line). (D) Residual analysis of standardized residuals versus standardized predicted values in the regression model of natural log-transformed tA versus polyQ-length showed an inverted U-shaped trend in the residual distribution (red line).