TABLE 1.

Criteria for Defining a Variant as Pathogenic

Criterion	Description and Significance
Nonsynonymous genetic variant	A genetic variant that alters the amino-acid sequence
Expression	Confirmation that the protein product of the gene is expressed in diseased tissue
Unbiased genetic analysis	Genome-wide analysis (linkage analysis, genome-wide association study, whole-exome or whole-genome sequencing) reduces the possibility of identifying a coincidental and unrelated mutation or a disease modifying mutation
Conservation	Conservation of the affected amino acid in different species through evolution suggests a critical biological role of that particular residue
Control population	Absence from a large number of unaffected controls, or confirmation of very low minor allele frequency in a population of interest demonstrates that the mutation is unlikely to be a polymorphism unrelated to the disease
Cosegregation	Demonstrates that the mutation is found in those with disease only (note: incomplete and age-dependent penetrance is common); identification of the disease phenotype in those without the mutation proves nonpathogenicity
Multiplicity of events	Demonstration that a variant may be causal in ≥2 unrelated probands greatly increases confidence in pathogenicity
Animal models	Recapitulation of the disease phenotype by the variant in animals genetically engineered to express the mutation strongly supports causality