When scientists analyze complex human diseases, such as cancer, a crucial step involves comparing the DNA sequence of a diseased individual to a reference genome from a healthy individual. This analysis helps identify genetic variations that may contribute to the disease, enabling researchers to accurately categorize the illness and understand its treatment responses.
Since the year 2000, the standard human reference genome has been incomplete, limiting researchers’ ability to access certain challenging genomic regions. This resulted in false positives, complicating the identification of true genetic variants responsible for tumor growth.
In 2022, the Society of Scientists announced a groundbreaking achievement: the first truly complete human genome, generated using advanced technology that minimizes fragmentation. This development has prompted extensive research into the benefits of utilizing new genomes in the study of complex genetic diseases, including cancer.
Researchers based in Canada and the United States proposed that employing the complete human genome could enhance the detection of structural variants, allowing for more accurate cancer diagnosis compared to traditional reference genomes. This analogy likens genomic mutations to missing or altered paragraphs in a textbook; structural mutations can lead to cancer by duplicating oncogenes, causing abnormal gene fusions, and inactivating tumor-suppressor genes.
To validate their hypothesis, researchers utilized established cancer cell models, specifically cancer cell lines alongside the cancer-free control known as COLO829. This particular cell line serves as a benchmark for evaluating new mutation detection methods. They analyzed multiple samples of the COLO829 cell line sequenced by different laboratories, as well as tumor samples from patients diagnosed with blood cancer, brain cancer, and ovarian cancer, thereby ensuring a real-world context for their findings.
The complete human reference genome incorporates approximately 200 million additional base pairs, effectively filling in gaps and rectifying missing regions from the previous standard. When the COLO829 sample was examined, the number of structural variants incorrectly identified using the outdated reference genome significantly decreased, from 225 to just 83 with the new genome. This advancement greatly enhances our capability to detect structural variations.
The research team noted that while the new human reference genome improves the precision of DNA change identification, it contains less labeled medical information compared to the older genome. To address this, they employed a tool called Levio SAM2 to align results from new and previous genomes, thereby combining the enhanced accuracy of new genomes with the extensive medical knowledge of older references, yielding optimal results.
The team applied this integrated approach to three patient samples and discovered that the number of cancer-specific mutation candidates needing manual clinical review was significantly reduced compared to using traditional reference genomes. This reduction streamlines the labor-intensive process of identifying true cancer-causing mutations, with one large variant, 609,000 base pairs in length, identified in a patient’s sample. This variant exhibited minimal signals in the old reference genome but displayed clear evidence in the new genome.
In conclusion, the researchers’ approach enhances structural mutation detection in cancer by minimizing false positives, allowing physicians to prioritize clinically significant mutations. They emphasized that lowering false positives is crucial in analyzing patient samples, and filtering out spurious mutations to isolate genuine cancer drivers requires considerable time and expertise. Although their liftover strategy increased analysis time by approximately 50% compared to solely using the old reference genome, researchers deemed this trade-off acceptable due to the considerable improvements in accuracy.
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Source: sciworthy.com
