"Rare variants" refers to genetic differences or mutations that occur infrequently within a population. These variations are not as common as the more typical or common versions of genes. Full definition
A key step in the analysis of rare variants in disease is to distinguish genetic variants that are likely to disturb gene function. (tllab.org)
It is clear that the risk of common diseases in our society is accounted for by both common and rare variants in the sequence of the genome. (decode.com)
The hunt continues for rare variants that can explain more severe cases. (sciencedaily.com)