Samples sent as DNA from external sites were extracted using different methods. Remaining samples (376) were extracted at UPenn from frozen brain tissue or blood. Genomic DNA was extracted from frozen brain tissue (50 mg) by the Qiagen MagAttract DNA Mini M48 Kit on the M48 BioRobot. Genomic DNA was purified from whole blood using FlexiGene kit (Qiagen). High quality DNA was required for the Illumina genotyping. All DNA samples were evaluated for purity by spectrophotometric analysis (Nanodrop) and for degradation by 1% agarose gel electrophoresis (Invitrogen).
