UMIs (Unique Molecular Identifiers), also known as "molecular barcodes", were introduced in Next-generation Sequencing (NGS) experiments for the first time more than a decade ago. These codes consist of different short oligonucleotide sequences that are uniquely added to each DNA molecule prior to library preparation in order to create a distinct identity for each molecule. After sequencing, it is possible to accurately identify the copies produced during PCR from each DNA fragment, as they have identical alignment and UMI sequence coordinates. Since each starting nucleic acid is labeled with a unique molecular barcode, the bioinformatics software is able to filter out possible errors produced during library generation and sequencing with a high level of accuracy and analyze only the correct reads.
UMIs are used for a wide range of NGS applications, but are especially valuable for the identification of low-frequency variants in genomic studies Whole Genome Sequencing (WGS), Whole Exome Sequencing (WES) and gene panels, as reducing the number of false positive variants increases the sensitivity of variant detection. In addition, they are highly recommended in samples in which many PCR cycles are required to obtain sufficient material for sequencing, as in the case of single cell studies. However, UMIs are also used in other types of experiments, such as the RNA-Seqas they are an excellent tool for quality control of the library and increase the accuracy of the results.
Thanks to its advantages, this methodology, which is increasingly in demand, promises to revolutionize the non-invasive early diagnosis of some diseases such as cancer.
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