Statistical analysis in genetic imprinting on the X chromosome and DNA forensics

Abstract

Genetic imprinting is an epigenetic phenomenon in which the expression of an allele copy depends on its parental origin. This mechanism has been found to play an important role in many complex diseases. Statistical tests for imprinting effects have been developed for more than fifteen years, but they are only suitable for autosomes. It is not until recently that the parental-asymmetry test on the X chromosome (XPAT) has been proposed to test for imprinting effects. However, this test can only be used for qualitative traits. A class of PAT-type tests are proposed to test for imprinting for quantitative traits on the X chromosome in the presence of association, namely, Q-XPAT($c$), Q-1-XPAT($c$) and Q-C-XPAT($c$), where $c$ is a constant. These methods can accommodate complete and incomplete nuclear families with an arbitrary number of daughters. Extensive simulation studies demonstrate that the proposed tests control the size well under the null hypothesis of no imprinting effects and are powerful under various family structures. Moreover, by setting the inbreeding coefficient in females to be nonzero and using the assortative mating pattern in simulations, the proposed tests are shown to be valid under Hardy-Weinberg disequilibrium. %190

Statistical analysis plays a crucial part in the evaluation of DNA evidence in forensic problems, including parentage determination. In this study, the accuracy of parentage testing of child trafficking cases is evaluated by considering the exclusion probability and likelihood ratio approach utilized in parentage determination. The situation of child trafficking in China is presented, with introduction to the national anti-trafficking DNA database established by the Chinese government to help reunite missing children with their families. The derivations of the probability for excluding a random individual or a random couple from parentage are given, with extension to allow for mutations. The accuracy of parentage testing of child trafficking cases is assessed using the exclusion probability and simulations based on likelihood ratio. Specifically, the number of random matches is calculated by employing the exclusion probability and the true positive rate and the false positive rate are analyzed by the likelihood ratio method.