TBX1 and Williams syndrome: The samples of the two groups with the deletion syndromes also showed similar SD frequencies for RB1 (P > 0.80), which were significantly higher than the corresponding RB1 value observed in the control group of samples (P < 10-6 and P < 10-4, for DGS/VCFS and Williams syndromes, respectively) (Table 1; Figure 3a, c and Figure 3e; Figure 4a).