DNA samples are readily obtainable from multiple sites although most studies use peripheral blood lymphocytes from venous samples. Some studies use samples from the oral cavity (buccal scrapings or epithelial cells in saliva) but these samples can be plagued by lesser DNA quantity, inferior DNA quality, and interference of DNA from oral microbial flora. Some samples are derived from lymphocytes transformed by Epstein-Barr virus into immortalized cell lines but such samples can have artifacts that complicate some analyses (e.g., trisomy 12 in copy number analyses). Although some investigators advocate using DNA pooling due to lower cost (i.e., genotyping aggregated cases and aggregated controls), this approach can have serious issues with accuracy and reliability and has not entered wide usage.
