The low-template-DNA (stochastic) threshold—Its determination relative to risk analysis for national DNA databases

Abstract 

Although the low-template or stochastic threshold is in widespread use and is typically set to 150–200rfu peak height, there has been no consideration on its determination and meaning. In this paper we propose a definition that is based upon the specific risk of wrongful designation of a heterozygous genotype as a homozygote which could lead to a false exclusion. Conversely, it is possible that a homozygote {a,a} could be designated as {a,F} where ‘F’ is a ‘wild card’, and this could lead to increased risk of false inclusion. To determine these risk levels, we analysed an experimental dataset that exhibited extreme drop-out using logistic regression. The derived probabilities are employed in a graphical model to determine the relative risks of wrongful designations that may cause false inclusions and exclusions. The methods described in this paper provide a preliminary solution of risk evaluation for any DNA process that employs a stochastic threshold.

Keywords: STR, Extreme drop-out, Low-level-DNA (stochastic) threshold, National DNA database, Low-copy-number