Process of defining pathogenicity of mutations

The task

Determining whether a genetic variant is disease-causing (pathogenic) follows a structured, evidence-based classification process, not a single definitive test - the ACMG/AMP framework is the most widely used standard
Formal variant classification has become increasingly standardised as genetic testing has expanded, given the need for consistent interpretation across different laboratories and clinicians

Multiple independent evidence streams are combined: population frequency (very common variants are unlikely to be highly penetrant disease-causing), computational/in silico predictions (effect on protein structure/function), functional studies (laboratory evidence of altered protein function), segregation (does the variant track with disease through an affected family?), and de novo occurrence (a new variant, absent in unaffected parents, in a patient with a consistent phenotype - strong evidence of pathogenicity)

Evidence is weighted and combined into a five-tier classification: pathogenic, likely pathogenic, variant of uncertain significance (VOUS), likely benign, benign - reflecting the overall strength and direction of the combined evidence, not any single criterion alone
No single piece of evidence (e.g. a computational prediction alone) is normally sufficient to classify a variant as pathogenic - multiple independent lines of evidence pointing the same direction are required

Classification directly determines clinical action - a "likely pathogenic" or "pathogenic" result supports acting on it clinically (surveillance, treatment, cascade testing), while a VOUS should not be acted upon in the same way (see variants of uncertain significance)
Classifications are living, not fixed - as new evidence accumulates (population databases grow, functional studies are published), variants can be reclassified over time, sometimes years after the original report

ACMG/AMP variant classification framework, variants of uncertain significance, cascade testing following a pathogenic finding

Pathogenicity is a probabilistic, evidence-weighted determination rather than a binary biological fact known with certainty - this is why classifications can and do change as evidence accumulates, and why laboratories periodically re-review previously reported variants

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