Why is population allele frequency important in variant classification, and which database is commonly used?

• A. Common variants in the population are unlikely pathogenic; gnomAD is widely used.
• B. Rare variants are always pathogenic.
• C. Population frequency is not used in interpretation.
• D. ClinVar is the only database used for frequency.

Answer: (A)

Population allele frequency helps you judge how likely a variant is to cause disease by comparing how common it is in the general population to how rare the disease is. If a variant is found at a high frequency in the general population, especially above thresholds expected for a rare disorder, it’s unlikely to be the cause of that disorder. This principle is a key part of variant interpretation, guiding you toward benign classifications when common alleles are observed.

The database commonly used for this purpose is gnomAD, which collects allele frequencies from tens of thousands of exomes and genomes. It serves as the standard reference to see how often a variant appears in diverse populations, helping to filter out variants that are too common to explain a rare condition. In interpretation frameworks, frequency data from gnomAD (and similar resources) underpin criteria that label high-frequency variants as likely benign.

Other statements aren’t accurate because rare variants are not guaranteed to be pathogenic, population frequency data are essential in interpretation, and ClinVar documents clinical significance rather than serving as the primary frequency reference.