Simple screening method for copy number variations associated with physical features

Recent studies of copy number variations (CNVs) associated with physical features, such as body mass index, body height or bone length, have suggested that such CNVs could serve as markers in forensic cases involving unidentified individuals. However, the process of cataloging CNVs has been slow because of the cumbersome nature and low reliability of the procedures involved. Here we describe a simple quantitative real-time PCR (Q-PCR) method for screening of medicolegally useful CNVs, which does not require reference DNA with known copy number. The first step is to prepare a chimeric plasmid vector including one copy each of the single-copy gene-specific sequence as the internal standard, and the target CNV-specific sequence. To assess the validity of this new method, we analyzed CNVs in the LTBP1 and ETV6 gene regions, both of which are candidate CNVs associated with body height. The PCR efficiencies for the single-copy (reference) gene and the target CNV were similar, indicating that quantitation was reliable. Furthermore, simulated analysis of the LTBP1 CNV using mock samples prepared by mixing vectors in varying proportions showed that this analytical method allowed correct determination of the LTBP1 copy number. These results demonstrated that our simple method has considerable potential for screening of trait-related CNVs that would be useful for forensic casework.