XDP CCCTCT repeat expansion index in blood and brain regions. a Distribution of expansion indices ranked by median values in blood and brain regions. Box-whisker plots show median ± interquartile range (IQR) and dots show values in individual patient samples b Heatmap of expansion indices values in different individuals (rows), scaled (z-score) across brain tissues (columns). To avoid poor normalization during scaling, brain regions with fewer than 12 measures and individuals with fewer than 6 tissue samples were excluded (Additional File 2: Fig. S4). Brain regions with no measurement are represented as black boxes. Patient IDs are shown with modal cerebellar repeat lengths in parentheses. Note that modal repeat lengths were the same across tissues for an individual with a few exceptions (Additional file 1: Fig.S2). c Linear regression analyses showing relationships between CCCTCT repeat length and expansion index in each tissue. The regression equations shown in bold font highlight those tissues (blood, cerebellum, subthalamic nuclei, cingulate gyrus, temporal pole, occipital cortex) showing a significant association of expansion index with repeat length. Grey shaded areas show 95% confidence interval. Blood (n = 164), Cereb = cerebellum (n = 40), Cd = caudate (n = 17), SbN = substantia nigra (n = 19), ION = inferior olivary nucleus (n = 9), RN = red nucleus (n = 11), Med.Th = medial thalamus (n = 20), Hip = hippocampus (n = 19), Pu = putamen (n = 19), Lat.Th = lateral thalamus (n = 20), DCN = deep cerebellar nuclei (n = 21), STh = subthalamic nucleus (n = 8), Cin.Gyrus = cingulate gyrus (n = 20), BA9 = frontal cortex Brodmann area 9 (n = 21), Parietal Cx = parietal cortex (n = 20), Insula = insular cortex (n = 19), TmP = temporal pole (n = 20), Oc. Cx = occipital cortex (n = 24).