LAUSR

Chromosomal triplications can be classified into recurrent and nonrecurrent triplications. Most of the nonrecurrent triplications are embedded in duplicated segments, and duplication‐inverted triplication–duplication (DUP–TRP/INV‐DUP) has been established as one of the mechanisms of triplication. This study aimed to reveal the underlying mechanism of the TRP–DUP–TRP pattern of chromosomal aberrations, in which the appearance of moving averages obtained through array‐based comparative genomic hybridization analysis is similar to the shadows of the caldera volcano‐like pattern, which were first identified in two patients with neurodevelopmental disabilities. For this purpose, whole‐genome sequencing using long‐read Nanopore sequencing was carried out to confirm breakpoint junctions. Custom array analysis and Sanger sequencing were also used to detect all breakpoint junctions. As a result, the TRP–DUP–TRP pattern consisted of only two patterns of breakpoint junctions in both patients. In patient 1, microhomologies were identified in breakpoint junctions. In patient 2, more complex architectures with insertional segments were identified. Thus, replication‐based mechanisms were considered as a mechanism of the TRP–DUP–TRP pattern.