In a recent study, researchers examined blood samples from 424 patients who had not received a diagnosis despite undergoing whole-genome sequencing. These patients had rare diseases and had already had their entire genetic code analyzed as part of the 100,000 Genomes Project in England, but no conclusive genetic cause had been identified. Whole-genome sequencing had been performed, but it had not provided a clear answer—essentially, the DNA was present but not revealing the underlying disease mechanism. To uncover more clues, the researchers measured nearly 1,500 proteins in the patients' blood. This approach helped confirm 13 diagnoses and identified 23 additional genetic leads that were previously unclear. Genetic variants, or changes in the DNA, do not always indicate a disease. Some may be harmless, while others might be responsible for a condition, or their role could be unknown. Variants of uncertain significance are particularly challenging to interpret because DNA alone does not always show their biological impact. Proteins, on the other hand, are the products of gene activity. If a gene is damaged, it can lead to an abnormal amount of protein in the blood. By measuring these proteins, researchers can detect whether a genetic variant is actually affecting the body, providing functional evidence of its role in disease. The study used a protein profiling test called the Olink Explore 1536, which measures 1,463 different proteins in blood serum. In 13 patients, abnormally low levels of certain proteins (detected as a z-score below -2) confirmed genetic diagnoses or provided new directions for further genetic analysis. For 23 other patients, the findings suggested potential links between specific genes and their conditions, even if the diagnosis was not yet clear. One example involved a rare mutation in the TIE1 gene, which was only found in a patient and his father, both of whom had a similar heart condition. The low protein levels in their blood provided strong evidence that the mutation was connected to the disease. While the results are promising, the researchers emphasize that this method is not a universal solution. Current technology only measures a fraction of the proteins in the human body, and not all disease-related proteins can be reliably detected in the blood. Additionally, not all harmful genetic variants affect protein levels. For now, this approach is more of a specialized tool used in research rather than a routine diagnostic test. Athanasios Kousathanas, a data scientist at Genomics England, noted that understanding which genetic variants contribute to rare diseases remains a significant challenge. Protein data complement genetic sequencing, but they do not replace it. Before this method can be widely used in clinical settings, improvements in technology and the development of reliable reference data will be needed. For now, most patients will continue to rely on traditional genetic testing and reanalysis for their diagnoses.