Synthetic nucleic acid control molecules
The present invention provides synthetic DNA strands that find use as controls or in nucleic acid testing methods. In particular, provided herein are synthetic DNA strands of known composition for use as control molecules in stool DNA testing, e.g., of mutations and/or methylation of DNA isolated from stool samples.
1. A method of characterizing a DNA test sample, comprising:
a) providing a run control composition comprising:
i) a first synthetic DNA fragment comprising a methylation footprint nucleotide sequence of a human gene, the methylation footprint nucleotide sequence in said first synthetic DNA fragment comprising a pattern of cytosines, wherein each of the cytosines within the methylation footprint nucleotide sequence comprises a 5-methyl;
ii) a second synthetic DNA fragment comprising the methylation footprint nucleotide sequence of the human gene, the methylation footprint nucleotide sequence in the second synthetic DNA fragment comprising the same number and pattern of cytosines as the methylation footprint nucleotide sequence in the first synthetic DNA fragment, wherein none of the cytosines within the methylation footprint nucleotide sequence in the second synthetic DNA fragment comprises a 5-methyl, and
iii) fish DNA;
wherein a ratio of the of the number of copies of the first synthetic DNA fragment to the number of copies of the second synthetic DNA fragment in the run control composition produces a run control expected result when assayed in a methylation assay;
b) providing a DNA test sample isolated from a human subject;
c) applying the methylation assay to the run control composition to produce run control experimental data;
d) applying the methylation assay to the DNA test sample to produce test sample experimental data; and
e) classifying the test sample experimental data as valid if the run control experimental data are within a pre-defined acceptable range relative to the run control expected result.
2. The method of claim 1 , wherein the methylation assay is a diagnostic assay that provides a diagnostic result from a DNA test sample by measuring a ratio of an amount of the human gene in the DNA test sample that is methylated in the methylation assay footprint nucleotide sequence to an amount of the gene in the DNA test sample that is not methylated in the methylation assay footprint nucleotide sequence.
3. The method of claim 2 , wherein a ratio in a DNA test sample above a cutoff value measured by the diagnostic assay is indicative of a disease state in the human subject.
4. The method of claim 3 , wherein the ratio of the number of copies of the first synthetic DNA fragment to the number of copies of the second synthetic DNA fragment in the run control composition is above said cutoff value.
5. The method of claim 1 , wherein the methylation assay comprises treating DNA with bisulfite.
6. The method of claim 1 , wherein the first synthetic DNA fragment and the second synthetic DNA fragment are from 50 to 500 base pairs in length.
7. The method of claim 1 , wherein the first synthetic DNA fragment and the second synthetic DNA fragment are double-stranded.
8. The method of claim 1 , wherein the ratio of the number of copies of the first synthetic DNA fragment to the number of copies of the second synthetic DNA fragment is greater than 0.01.
9. The method of claim 1 , wherein the ratio of the number of copies of the first synthetic DNA fragment to the number of copies of the second synthetic DNA fragment is from 0.02 to 0.3.
10. The method of claim 1 , wherein said fish DNA is present in a concentration of at least 20 μg/mL.
11. The method of claim 1 , wherein the first synthetic DNA fragment and the second synthetic DNA fragment comprise a nucleotide sequence from one or more of BMP3 and NDRG4.
12. The method of claim 1 , wherein the run control composition further comprises a synthetic DNA fragment comprising a sequence from a human reference gene.
13. The method of claim 12 , wherein the synthetic DNA fragment comprising a sequence from a human reference gene comprises a sequence from (3-actin.
14. The method of claim 1 , wherein the methylation assay comprises an invasive cleavage assay.
15. The method of claim 14 , wherein the invasive cleavage assay is a flap assay.
16. The method of claim 15 , wherein the flap assay comprises one or more reagents selected from the group consisting of an invasive oligonucleotide, a flap oligonucleotide, a flap endonuclease, and a FRET cassette.
17. The method of claim 1 wherein the methylation assay is applied to the run control composition and to the DNA test sample in separate reaction mixtures.
18. The method of claim 17 , wherein the separate reaction mixtures are in separate wells in a single microwell plate.
19. The method of claim 17 , wherein the reaction mixtures comprise one or more of DNA polymerase, deoxynucleoside triphosphates, amplification buffer, primer oligonucleotides, probe oligonucleotide, and magnesium salt.
20. The method of claim 1 , wherein the DNA test sample is isolated from stool or a bodily fluid.