Sequence changes can be very complex, involving a range of changes at one specific location. Complex changes, including translocations, should be described using the recommendations of the accepted HGVS nomeclature named extension ISCN (see SVD-WG004 (ISCN<>HGVS)). The ISCN extension has been developed in collaboration with and are based on those of the 2016 Standing Committee on Human Cytogenomic Nomenclature (ISCN), covering the description of numerical and structural chromosomal changes detected using microscopic and cytogenetic techniques. It should be noted there is a basic difference between ISCN and HGVS. While ISCN describes more the structure of the resulting chromosome(s), HGVS describes the variant(s) detected.
NOTE: In ISCN it is allowed to describe positions using the format “108,111,982”, HGVS only allows “108111982”.
NOTE: The description of complex changes can become rather complicated and at some point, although literally correct, effectively meaningless.
The basis of the examples is from Community Consultation proposal SVD-WG004. To simplify descriptions genomic reference sequences may be indicated as “chrX” (representing NC_000023.11 (hg38)). For the HGVS descriptions we only use full reference sequence identifiers. Note that in HGVS the variant detected is described, while ISCN describes more the structure of the resulting chromosome(s).