Allele frequency data is important for variant prioritisation – it helps to identify variants that are less likely to be causing a phenotype or disease. With the Ensembl VEP, you can get allele frequencies for variants that are identical with the variants you analysed and you can use allele frequencies to filter the results of your analysis.

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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. 

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If you are filtering a set of variants to look for those potentially involved in disease, your first stop will probably be databases of phenotype associations, like ClinVar. There is also a lot of valuable information on variant-disease associations in the literature, which may not yet have been extracted into curated databases. It can be hard to compile lists of citations for a large set of variants, but Ensembl VEP is here to help! 

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