This is regarding MTHFR C677T mutation detection by Single Nucleotide Primer Extension assay. My snapshot primer is 34 mer and when I did a Primer Focus Reaction I got C at 34.5 and T/A/G in the range of 43-44. I did about 10 clinical specimens and have got all the wild type specimens i.e. C at 34.5 and mutants i.e. T at 43.4. All the results were confirmed by sequencing. I fail to understand how a primer that is 34 mer shows mutant peak at 43.4 (almost 9 bp away) in the electropherogram. My exposure to snapshot assays is minimal. I am very interested to hear the opinions of others regarding this.