Patent ID: 7824852

Claim:
A method for detecting the methylation status of a cytosine position in genomic DNA samples, comprising: a) chemically treating a genomic DNA from a DNA sample with a reagent whereby 5-methylcytosine and cytosine react differently to said reagent, thus exhibiting different base pairing behaviors in the DNA duplex subsequent to the chemical treatment, b) amplifying the chemically treated DNA using a polymerase and at least one oligonucleotide (type A) as a primer, c) hybridizing the amplified genomic DNA to two oligonucleotides (type B) specific for DNA treated according to step (a) wherein (i) the 3′-ends of the oligonucleotides (type B) hybridize to the position to be analyzed with regard to its methylation in the genomic DNA sample (ii) the oligonucleotides (type B) are bonded to a solid support, and (iii) one oligonucleotide (type B) gives rise to complete complementarity in case of methylation while the other oligonucleotide gives rise to complete complementarity in case of non-methylation; d) elongating the one of the two oligonucleotides (type B) that has previously hybridized with its 3′-end to the position to be analyzed without mispairings by up to a maximum of ten nucleotides by means of a polymerase and a mixture of nucleotides wherein the elongation depends on the methylation status of the specific cytosine in the genomic DNA sample, wherein said mixture of nucleotides is either a mixture consisting of the nucleobases A, T, and C or a mixture consisting of the nucleobases G, A and T, wherein at least one of said nucleobases in said mixture is detectably labeled; e) comparing the signals derived from both oligonucleotides (type B) and deducing therefrom the methylation status of said cytosine position.