We present a unique way to detect base-pair mismatches in DNA, leading to a different epigenetic disorder by the method of nanopore sequencing. Based on a tight-binding formulation of a graphene nanopore device, using the Green’s function approach we study the changes in the electronic transport properties of the device as a double-stranded DNA translocate through the nanopore embedded in a zigzag graphene nanoribbon. In the present work we are not only successful in detecting the usual AT and GC pairs but also a set of possible mismatches in the complementary base pairing.