Institution: | Richard Gallon,Barbara Mühlegger,Sören‐Sebastian Wenzel,Harsh Sheth,Christine Hayes,Stefan Aretz,Karin Dahan,William Foulkes,Christian P. Kratz,Tim Ripperger,Amedeo A. Azizi,Hagit Baris Feldman,Anne‐Laure Chong,Ugur Demirsoy,Benoît Florkin,Thomas Imschweiler,Danuta Januszkiewicz‐Lewandowska,Stephan Lobitz,Michaela Nathrath,Hans‐Jürgen Pander,Vanesa Perez‐Alonso,Claudia Perne,Iman Ragab,Thorsten Rosenbaum,Daniel Rueda,Markus G. Seidel,Manon Suerink,Julia Taeubner,Stefanie‐Yvonne Zimmermann,Johannes Zschocke,Gillian M. Borthwick,John Burn,Michael S. Jackson,Mauro Santibanez‐Koref,Katharina Wimmer |
Abstract: | Constitutional mismatch repair deficiency (CMMRD) is caused by germline pathogenic variants in both alleles of a mismatch repair gene. Patients have an exceptionally high risk of numerous pediatric malignancies and benefit from surveillance and adjusted treatment. The diversity of its manifestation, and ambiguous genotyping results, particularly from PMS2, can complicate diagnosis and preclude timely patient management. Assessment of low‐level microsatellite instability in nonneoplastic tissues can detect CMMRD, but current techniques are laborious or of limited sensitivity. Here, we present a simple, scalable CMMRD diagnostic assay. It uses sequencing and molecular barcodes to detect low‐frequency microsatellite variants in peripheral blood leukocytes and classifies samples using variant frequencies. We tested 30 samples from 26 genetically‐confirmed CMMRD patients, and samples from 94 controls and 40 Lynch syndrome patients. All samples were correctly classified, except one from a CMMRD patient recovering from aplasia. However, additional samples from this same patient tested positive for CMMRD. The assay also confirmed CMMRD in six suspected patients. The assay is suitable for both rapid CMMRD diagnosis within clinical decision windows and scalable screening of at‐risk populations. Its deployment will improve patient care, and better define the prevalence and phenotype of this likely underreported cancer syndrome. |