Genotyping of three candidate genes afte ... DNA collected from buccal cells

The amount of genomic DNA obtained from buccal cell methods may be suboptimal for large-scale genetics projects, because the quantity of DNA may be insufficient for the number of analyses proposed. Primer extension preamplification (PEP) methods that can amplify the entire genome 100-fold or more, offer a potential solution to this problem. We compared PEP buccal DNA with genomic buccal DNA from 315 individuals from 97 families of the Colorado Longitudinal Twin Study for three loci: the dopamine transporter, dopamine D4 receptor, and serotonin transporter. A total of 1890 genomic and 1890 PEP alleles were assessed, and 1670 comparisons (88%) agreed after a single determination. Fifty-three individuals had one or more failed initial polymerase chain reactions (PCR), with 81 failed PCRs in total, accounting for 162 missing allele calls. The failed PCRs were repeated once, and 146 of the missing allele calls were recovered. Comparisons between genomic and PEP DNA allele calls showed 37 individuals had one or more discrepancies, for a total of 52 inconsistencies. Of these, the initial PEP result was found to be correct in 18 cases, the initial genomic result was found to be correct in 25 cases, and 9 could not be resolved. Overall, rates of true calls, missing data, and genotyping errors for genomic and PEP DNA samples were nearly identical: of the 1890 genotypes assessed, true calls were found in 1845 genomic and 1840 PEP samples, missing genotypes in 18 genomic and 16 PEP samples, and incorrect assignments in 18 genomic and 25 PEP samples. These results suggest that routine whole-genome preamplification of genomic DNA is an appropriate method for providing DNA to genotype these loci.