A modified Chelex-based method using an InstaGene whole blood kit (Bio-Rad Laboratories, Hercules, CA) was used to extract DNA from blood spots on filter paper. A blood spot of 4 mm in diameter was punched out and soaked overnight in 100 μl of phosphate-buffered saline (PBS) at 4°C. DNA extraction was performed on the following day as described previously (1). All samples were purified twice with the InstaGene matrix and stored at −20°C until further processing.
A template of 5 μl was used in a 50-μl nest 1 reaction mixture (GoTaq PCR core system; Promega, Madison, WI) under the following conditions: 5 μl of each primer (10 μM), 125 μM each dNTP, 2 mM MgCl2, and 1 U of GoTaq DNA polymerase.
Nest 2 reactions and further procedures (with the exception of the centrifugation step of the direct PCR nest 1 product) were identical to the standard- and direct nested-PCR techniques discussed above.