Researchers’ understanding of certain rare diseases is changing as new sequencing technology is providing new views of the genome. A group of diseases collectively known as “repeat expansion disorders” including Fragile X Syndrome, Freidrich’s Ataxia, and Huntington’s disease are being viewed in new ways thanks to the ability to read long fragments of DNA. We spoke to Jonas Korlach, chief scientific officer of Pacific Biosciences, about the company’s sequencing technology, how its changing the understanding of diseases thought to be well understood, and how it may lead to improved diagnostics and therapeutics.