7: Using high-resolution variant frequencies to empower clinical genome interpretation

Whiffin N et al., Genetics in Medicine - A statistical framework uses large reference allele-frequency data (ExAC) together with disease prevalence, heterogeneity, penetrance, and sampling variance to set rigorous frequency filters that improve Mendelian variant interpretation. Key terms: allele frequency, clinical genomics, ExAC, inherited cardiovascular conditions, variant interpretation.

Study Highlights:
The authors develop a two-step statistical framework to compute a disease-specific maximum credible population allele frequency and a maximum tolerated allele count accounting for prevalence, genetic and allelic heterogeneity, inheritance mode, penetrance, and sampling variance. Applying this to hypertrophic cardiomyopathy and other inherited cardiac conditions using ExAC, stringent thresholds (well below 0.1%) remove roughly two-thirds of candidate protein-altering variants per exome. Validation against curated ClinVar and case series shows true pathogenic variants are retained while many likely benign or unsupported variants are reclassified. The group provides precomputed filtering allele frequencies for ExAC and an online calculator and code to apply the approach.

Conclusion:
A disease-aware, statistically principled allele-frequency filtering framework and precomputed ExAC thresholds materially reduce candidate variant lists and improve clinical genome interpretation without discarding true pathogenic variants.

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2025-04-17.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music

QC Summary:
- factual score: 10/10
- metadata score: 10/10
- supported core claims: 6
- claims flagged for review: 0
- metadata checks passed: 4
- metadata issues found: 0

Metadata Audited:
- article_doi
- article_title
- article_journal
- license

Factual Items Audited:
- The article presents a two-stage statistical framework to assess whether a disease-associated variant is too common, incorporating disease prevalence, genetic/allelic heterogeneity
- Maximum credible population AF for a pathogenic variant is defined as prevalence × maximum allelic contribution × 1/penetrance (with a separate formula for recessive diseases).
- Using hypertrophic cardiomyopathy (HCM) as an exemplar, prevalence ~1/500, max allelic contribution ~0.02, penetrance ~0.5 yields max credible AF ~4×10^-5.
- Maximum tolerated ExAC allele count for HCM is 9, given AN ≈ 121,412 and 50% penetrance; this led to threshold of 9 with observed 3 in ExAC for a pathogenic variant MYBPC3 c.1504C>
- The approach reduces the number of candidate variants per exome by about two-thirds (from ~176 to ~63) and retains 99.6% of true pathogenic variants for HCM.
- The framework can be extended to recessive diseases; example PCD yields maximum tolerated ExAC AC of 322; a variant with AC 2306 observed in NME8 is too common to cause disease.

QC result: Pass.