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Human retrocopies, i.e. mRNA transcripts benefitting from the LINE-1 machinery for retrotransposition, may have specific consequences for genomic testing. NGS techniques allow the detection of such mobile elements but they may be misinterpreted as genomic duplications or be totally overlooked. We report eight observations of retrocopies detected during diagnostic NGS analyses of targeted gene panels, exome, or genome sequencing. For seven cases, while an exons-only copy number gain was called, read alignment inspection revealed a depth of coverage shift at every exon-intron junction where indels were also systematically called. Moreover, aberrant chimeric read pairs spanned entire introns or were paired with another locus for terminal exons. The 8th retrocopy was present in the reference genome and thus showed a normal NGS profile. We emphasize the existence of retrocopies and strategies to accurately detect them at a glance during genetic testing and discuss pitfalls for genetic testing. This article is protected by copyright. All rights reserved.

Original publication




Journal article


Hum Mutat

Publication Date



Genome mobility, Retrocopies, copy number gain, genetic testing pitfalls