Ultra high resolution oligonucleotide array analysis. Results of ultra high resolution oligonucleotide array analysis of the 17q21.31 microdeletion proximal breakpoint (mean probe density 1 probe/5.2 bp). (A) Data from a 50 kb region (chr17:41025000–41075000, hg17) in five unrelated 17q21.31 deletion patients and one control. In each deletion, the proximal breakpoint occurred in a segmental duplication of length, 34.2 kb, identity 98.7% (chr17:41026709–41060948). (B) Zoomed view showing a 5 kb region (chr17:41044500–41049500). All five patients have breakpoints which are indistinguishable, mapping to within an interval of <500 bp contained within an L2 LINE motif. The highly variable dynamic response of certain probes in this region to report the deletion is likely a result of their different sequence properties (38). For each individual, deviations of probe log2 ratios from zero are depicted by grey/black bars, with those exceeding a threshold of 1.5 standard deviations from the mean probe ratio coloured green and red to represent relative gains and losses, respectively. Tracks above each plot indicate segmental duplications (grey/yellow bars represent duplicons with 90–98%/98–99% sequence identity, respectively).