Concordance of Whole-Genome Long-Read Sequencing with Standard Clinical Testing for Prader-Willi and Angelman Syndromes

Current clinical testing approaches for individuals with suspected imprinting disorders are complex, often requiring multiple tests performed in a stepwise manner to make a precise molecular diagnosis. We investigated whether whole-genome long-read sequencing could be used as a single data source to simultaneously evaluate copy number variants, single-nucleotide variants, structural variants, and differences in methylation in a cohort of individuals known to have either Prader-Willi or Angelman syndrome. Twenty-five individuals sequenced to an average depth of coverage of 36x on an Oxford Nanopore Technologies PromethION were evaluated. A custom one-page report was generated that could be used to assess copy number, single-nucleotide variants, and methylation patterns at select CpG sites within the 15q11.2-q13.1 region and prioritize candidate pathogenic variants in UBE3A. After training with three positive controls, three analysts blinded to the known clinical diagnosis arrived at the correct molecular diagnosis for 22 of 22 cases (20 true positive, 2 negative controls). Our findings demonstrate the utility of long-read sequencing as a single, comprehensive data source for complex clinical testing, offering potential benefits, such as reduced testing costs, increased diagnostic yield, and shorter turnaround times, in the clinical laboratory. (J Mol Diagn 2025, 27: 166e176; https:// doi.org/10.1016/j.jmoldx.2024.12.003)