High-Yield DNA-Based Neurofibromatosis Type 1 Diagnostics Reveal Population-Specific Mutation Landscape in 1917 Koreans.

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder with extensive allelic heterogeneity. Although RNA-based assays can increase sensitivity, their cost and complexity limit their routine use. A DNA-only tiered diagnostic approach was evaluated in 1917 unrelated Korean individuals with clinically suspected NF1. The process began with targeted sequencing of blood-derived genomic DNA, followed by reflex multiplex ligation-dependent probe amplification for copy number variants and a lesional tissue test for suspected mosaicism. Initial targeted sequencing of the NF1 gene established a diagnostic yield of 74.0%. The addition of reflex multiplex ligation-dependent probe amplification and tissue testing increased the cumulative yield to 79.2%. Subsequent post-report variant reclassification and whole-genome sequencing further increased the overall diagnostic yield to 81.6%. Among 901 distinct pathogenic variants identified-81.4% of which were private-truncating variants were predominant (79.0%). Notably, several variants enriched in European cohorts and with established genotype-phenotype correlations (eg, p.Arg1809Cys, p.Met992del, and p.Arg1276Gln) were rare in this cohort, highlighting population-specific differences. Individuals with large deletions were referred at younger ages, suggesting potential genotype-phenotype associations. These data demonstrate that a stepwise, DNA-only strategy delivers high yield and scalability for routine NF1 diagnostics, while delineating a Korean-specific mutational landscape. This practical workflow offers a robust alternative to RNA-based approaches in real-world clinical settings.