Breakpoints of gross deletions coincide with non-B DNA conformations (Bacolla et al., PNAS, 2004) Note (Comments by Robert Wells, JBC, 2009): This discovery was profound because it amalgamated the topics of DNA structure with human genetics along with bioinformatics and medicine. Breakpoints had been recognized for years to be important in the etiology of various translocations, but this discovery introduced the concept of non-B DNA conformations as signals for the specific breakpoints. This and subsequent work have revealed that slipped structures, cruciforms, triplexes, tetraplexes, and perhaps other non-B DNA structures, including left-handed Z DNA (Fig. 2), are formed in chromosomes and elicit far-reaching genetic consequences via recombination/repair. Repeating sequences, in their non-B conformations, cause gross genomic rearrangements (translocations, deletions, insertions, inversions, and duplications). These rearrangements are the genetic basis for numerous human genomic diseases, including polycystic kidney disease, adrenoleukodystrophy, follicular lymphomas, and spermatogenic failure. At least 70 diseases fall into this category.
Short, direct repeats at the breakpoints of deletions of the retinoblastoma gene (Canning and Dryja, PNAS, 1989) Note: This study identified many unique deletions in the retinoblastoma gene in germline DNA (some are homozygous deletions) and discovered many short, direct repeats at the breakpoints of deletions and argues against the existence of "hotspots" in these deletions. Most of these deletion cases have short insertions with the longest one 80 bp in size. It cites a "slipped mispairing" model to explain the formation of these deletions.