How do you design and validate ddPCR assays for rare variant detection?

Rare variant ddPCR assay design requires: primer/probe design avoiding SNPs in binding sites, optimal amplicon length (60-200bp), mutant-specific locked nucleic acid (LNA) probes for discrimination, careful thermal gradient optimization for maximal cluster separation, and wild-type background reduction strategies (restriction digestion, blocker oligonucleotides). Validation includes: limit of blank (LOB), limit of detection (LOD, typically 0.01-0.1%), linearity across relevant range, precision at low frequencies, and comparison to orthogonal methods (NGS, allele-specific PCR). Controls must include wild-type only, mutant spikes at various levels, and no-template controls. Analysis requires appropriate thresholds and statistical considerations for low counts. Applications include liquid biopsy, MRD monitoring, and CRISPR editing quantification.