Figure 4
Linear regression analysis of SCA6 and -7 based on the model. (A) A total of 132 SCA6 patients with expanded CAG repeats in the alpha-1A-calcium channel gene was analyzed. Inspection of logarithmically transformed mean age-at-onset versus CAG size plots identified 27–29 CAG repeats as relative outliers and showed the best fit to a quadratic curve. A regression analysis of natural log-transformed (tA2 - tE2)1/2 against CAG size provided the best fit to a linear model (-0.2567x + 9.553) when tE2 = 700. (B) A total of 188 SCA7 patients with expanded CAG repeats in the ataxin-7 gene was analyzed. Inspection of logarithmically transformed mean age-at-onset versus CAG size plots identified 38 and 75 CAG repeats as relative outlier. These data were therefore excluded from further study. A regression analysis of natural log-transformed (tA2 - tE2)1/2 against CAG size provided the best fit to a linear model (-0.0658x + 6.513) when tE2 = 30.