The lowercase “c.” is part of Human Genome Variation Society (HGVS) nomenclature (naming system) and tells you what reference sequence is being used to describe the genetic variant. Specifically, c. = coding DNA sequence.
Example: c.1286A>C
- c. = coding DNA reference sequence (HGVS nomenclature)
- 1286 = position in the coding DNA sequence
- A = reference nucleotide (adenine)
- >C = changed to cytosine
Read as: “At coding DNA position 1286, an adenine is replaced by a cytosine.”
Example: c.665C>T
- c. = coding DNA reference
- 665 = position in the coding sequence
- C = the reference nucleotide (cytosine)
- >T = changed to thymine
Read as: “At coding DNA position 665, a cytosine is replaced by a thymine.
Other common HGVS genome prefixes you may see on genetic reports:
- g. = genomic DNA sequence
- p. = protein-level change
- m. = mitochondrial DNA
- n. = non-coding RNA