Evaluation of instability index. (A) To assess the sensitivity of the instability index to the amount of input DNA we calculated instability indices using varying amounts of template DNA (HdhQ 111/, 5 months, striatum). The coefficient of variation (CV) of the striatal instability index was 2.2%, calculated by dividing the standard deviation of 4 instability index measurements (50, 100, 200, and 300 ng DNA) by the mean instability indices of same 4 measurements. (B) GeneMapper traces and instability indices from bulk DNA (100 ng) and frequency distributions of CAG repeat length obtained using small pool-PCR from striatum, cortex and spleen from an HdhQ 111/+mouse at 5 months of age. (C) Instability indices from bulk DNA (100 ng) GeneMapper traces were plotted against small pool instability indices (see Methods section) obtained from 9 tissues (striatum, cortex, cerebellum, liver, lung, stomach, skin, heart, ovary) of an HdhQ 111/+mouse at 5 months of age. The two values were highly correlated.