Figure 2.

Variant descriptions at exon/intron boundaries. This illustrates how a three‐base deletion in the COL1A2 gene at the junction of the 3′ end of exon 19 with the adjacent intron might be described in two different ways in the context of the RefSeq transcript reference sequence NM_000089.3. Description A shows that the three deleted bases can be described at position NM_000089.3:c.1033_1035 where the deleted bases are GTT, but Description B shows that the variant can be normalized and described at position NM_000089.3:c.1035_1035+2 where the deleted bases are TGT. The latter description corresponds with the genomic variant description NC_000007.13:g.94039133_94039135delTGT. Formally, intronic variants described in the context of a transcript reference sequence must be accompanied by a genomic reference sequence to allow full verification of the variant. This is illustrated by Description C