What do the letters 'p' and 'c' mean in mutation descriptions?
According to the HGVS guidelines, a letter prefix should be used to indicate the reference sequence used. Accepted prefixes are:


“g.” for a genomic reference sequence
“m.” for a mitochondrial reference sequence
“c.” for a coding DNA reference sequence
“n.” for a non-coding DNA reference sequence
“r.” for an RNA reference sequence (transcript)
“p.” for a protein reference sequence