Alu elements are short stretches of about 300 bp that are unique to the human genomic DNA (gDNA). There are over one million Alu elements interspersed throughout the genome constituting about 10.7% of the bases. The TATAA Alu Assays target consensus Alu sequences making them exceptionally sensitive for human gDNA. In fact, the assays are so sensitive that we rarely find a negative sample!
Ultrasensitive detection and semi-quantification of human genomic DNA
Most reagents, including master mixes, primers and probes, used for molecular analysis are contaminated with human gDNA from the manufacturing process. In most applications, this residual gDNA causes no problems. However, in studies of circulating cell free DNA, particularly when assaying for rare mutations or copy number variations, it can lead to false positive and erroneous results. Problem is even more serious in single and few cell applications including preimplantation genetic diagnostics (PGD) and preimplantation genetic screening (PGS).
Quality control of circulating cell free DNA
When analyzing circulating cell free DNA, it is critical the sample contains enough human gDNA for the measurement to be accurate. This is particularly important when assaying for rare mutations or variants, as the factor limiting sensitivity often is the total number of DNA copies in the sample.
The TATAA Alu assays are designed to target multiple copies to generate reliable results also for very low amount of human gDNA. Alu assays are available that produce different amplicon lengths, which makes it possible to assess also the length distribution of the gDNA present. For example, analyzing a sample with TATAA ALU-60 and TATAA ALU-187 assays, generating amplicons of 60 and 187 bp, respectively, the fraction of mononucleosomal fragments, expected to be the product of apoptosis, can be assessed.
Quantification of human genomic DNA
The amount of human gDNA in a sample can be determined by calibration against the TATAA Human Genomic DNA Secondary Standard (CHG50)