High fractions of exogenous DNA in human buccal samples reduce the quality of large-scale genotyping.

Buccal cell samples are considered a reliable source of DNA for genotyping studies. However, a potential drawback is the presence of exogenous DNA that is coextracted with human genomic DNA. A set of saliva and cheek swab samples, in which the fraction of human DNA varies from 10 to 96%, was genotyped using the Affymetrix Mapping 500 K Array. Samples containing less than 30% human DNA performed poorly in terms of accuracy and reliability. Therefore, we recommend quantitating the amount of human DNA in buccal samples to be used for large-scale genotyping and eliminating samples with less than 30% human DNA.