TBX1 and Williams syndrome: The considerably low frequency of SD cells for SNRPN found in the samples of the two groups of patients with the deletion syndromes were similar to each other (P > 0.05), but each deviated significantly from those characterizing the samples of the control group (P < 10-9 and P < 10-7, for DGS/VCFS and Williams syndromes, respectively) (Table 1; Figure 3b, d and Figure 3f; Figure 4a).