Introduction Approximately half of patients with severe haemophilia A are caused by structural variants in the F8 gene. Unlike inversions or deletions directly impairing the integrity of F8, some duplications do not completely disrupt the open reading frame or even retain an intact F8 copy. Currently, only a few duplication breakpoints were precisely characterized, and the corresponding rearrangement mechanisms and clinical outcomes remain to be further investigated. Aim Establishing an effective strategy for breakpoint characterization of duplications and revealing their rearrangement mechanisms. Methods AccuCopy is used for the detection of duplications, long‐distance PCR for the characterization of tandem duplications, genome walking technique and whole genome sequencing for the characterization of inverted duplications. Results Four F8 duplication rearrangements were successfully characterized at the nucleotide level: one tandem duplication (exons 7–11) and three inverted duplications (exons 7–22, exons 2–26, and exons 15–22). Two shared features of inverted duplication were found after carefully analysing our results and breakpoint information in the literature: 1, an inverted fragment was inserted into the original chromosome via two junctions; 2, one junction is mediated by a pair of inverted repetitive elements, while the other consists of two breakpoints with microhomology. Conclusion Similar breakpoint features motivated us to propose a DNA replication‐based model to explain the formation of duplication rearrangements. Based on our model, we further divide the inverted duplications into three basic types: type I with a DEL‐NOR/INV‐DUP pattern, type II with a DUP‐NOR/INV‐DUP pattern and type III with a DUP‐TRP/INV‐DUP pattern.

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ABSTRACT. Phosphatidylinositol-3-OH kinase and RAS-activated signaling pathways play an important role in tumor formation. Abnormalities in relevant genes play essential roles in the occurrence and development of many human cancers. Studies of breast cancer have mainly focused on the women in western countries, but few studies have examined the frequency of mutations in PIK3CA, BRAF, and KRAS in Chinese breast cancer patients. In this study, we conducted sequence analysis of PIK3CA, BRAF, and KRAS and determined relationships with the occurrence of breast cancer in women from Qinghai. DNA was extracted from 25 cases of human breast cancer tissue samples. PIK3CA, BRAF, and KRAS mutation analysis was performed by polymerase chain reaction and DNA sequencing. No mutations were found in PIK3CA, BRAF, and KRAS of adjacent tissues. However, PIK3CA mutations were observed in 32% (8) of the 25 breast cancer tissues examined, in which exon 9 accounted for 4% (1), exon 20 accounted for 28% (7), and no mutations were found in exon 1 of PIK3CA. Sequencing of exon 2 of KRAS suggested that 20% (5) of the 25 samples harbored a mutation and 16% (4) 14840-14846 (2015) harbored a mutation. Any mutation in these 3 oncogenes may induce the occurrence and development of breast cancer.