PE: What is the long-read method, and how does it impact the rare disease space?
Musone: Short-read approaches fragment DNA into small pieces and computationally reconstruct the genome against a reference – this can obscure complex regions and structural variation. In contrast, long-read WGS analyzes extended stretches of native DNA in a single pass, preserving genomic context and improving accuracy across repetitive or structurally complex regions.
This difference in sequencing technology is especially important for detecting pathogenic variants in rare diseases. Many of these variants involve repeat expansions, structural rearrangements, copy number changes, or reside in so-called “dark” regions of the genome that short reads struggle to resolve. Long-reads span entire repeat regions, determine whether variants occur on the same maternal or parental chromosome through phasing, and detect epigenetic signatures all within the same workflow.
This visibility increases diagnostic yield and consolidates multiple legacy assays into a single genome-wide test. As sequencing costs decrease and throughput increases, long-read WGS is becoming an increasingly viable earlier step in the rare disease diagnostic pathway.
PE: Where has long read been proven transformative?
Musone: Long-read WGS has already transformed rare disease research and clinical investigation. Research led by Radboud University Medical Center illustrated that advanced long-read sequencing could replace multiple diagnostic tests with a single complete run. In this study, HiFi WGS identified 93% of pathogenic variants in a cohort of challenging rare disease cases and detected genetic variants that had been missed by short-reads, including complex structural changes and DNA methylation abnormalities.
Collaborative initiatives such as the Undiagnosed Hackathon have also highlighted the value of HiFi sequencing. By combining international expertise with long-read technology, potential diagnoses were identified for 10 previously unsolved cases within two days, offering new hope to families who had spent years looking for answers.
Beyond rare disease, long read WGS has made significant strides in understanding the human genome. In 2022, the Telomere-to-Telomere (T2T) Consortium used HiFi long reads to publish the first fully complete human genome, revealing nearly 200 million base pairs of previously missing sequence. This complete reference genome will help scientists identify disease‑associated variants and better understand genetic diseases and human biology.
PE: What complications do patients around the world face in receiving testing for rare diseases?
Taft: Unfortunately, patients with rare genetics still face considerable hurdles. These disorders are under-recognized, and the first challenge a patient with a rare disorder often is having the healthcare system identify them as someone who may have a genetic disorder and therefore could benefit from genomic testing. Access to testing varies dramatically. In many low- and middle-income countries, advanced sequencing is simply unavailable. Even in wealthy, nationalised health systems, comprehensive testing is still often gated by funding, extensive wait time and insufficient interpretation capacity.
As a result, patients can wait years for a diagnosis, and many will never receive one. Without a diagnosis, families lack clarity about prognosis, disease management, and recurrence risk, and patients may be excluded from clinical trials or targeted therapies. It is essential that we to shorten the diagnostic odyssey and improve outcomes for rare disease patients worldwide.