Nanopore long-read sequencing for the critically ill facilitates ultrarapid diagnostics and urgent clinical decision making.

Critically ill pediatric patients often have genetic disorders requiring a rapid diagnosis to guide urgent care decisions. Standard genetic testing typically takes weeks and requires multiple tests. Nanopore long-read genome sequencing (LR-GS) delivers genome-wide results within days as a one-test-fits-all solution. As one of the first centers in Europe, we implement ultrarapid LR-GS for critically ill patients. We enrolled 26 critically ill patients (median age 2 months) suspected of having a genetic disorder at the intensive care unit to perform (ultra)rapid nanopore LR-GS alongside standard genomic care. We compared diagnostic yield, turnaround time (TAT), and evaluated the impact on clinical decision making. In 11/26 cases a genetic diagnosis was made with (ultra)rapid LR-GS. From sample receipt to result, the average TAT was 5.3 days (range 2.0-10.8) for LR-GS and 18.4 days (range 6.1-29.1) for standard genomic care. DNA methylation analysis from LR-GS expedited the diagnosis in 3/26 cases. In 7/11 solved cases ultrarapid LR-GS led to immediate adjustments in patient care, e.g., medication switch or termination of treatment. Our findings underscore the clinical impact of ultrarapid LR-GS, including added value of methylation analysis, for critically ill patients and highlight existing challenges, paving the way to ultrarapid LR-GS integration into standard diagnostics.