Variants can be represented in myriad different ways; indeed, Ensembl VEP currently supports input in many different formats, including VCF, HGVS and SPDI. However, even within these specifications, variants can be described ambiguously. Insertions and deletions within repeated regions can be described at multiple different locations. For example, VCF describes variants using their most 5’ representation, while HGVS format describes a variant at its most 3’ location.
Starting in Ensembl 100, VEP optionally normalises variants within repeated regions by shifting them as far as possible in the 3’ direction before consequence calculation. This standardises VEP output for equivalent variant alleles which are described using different conventions.