Detection of CAG repeats in pre-eclampsia/eclampsia using the repeat expansion detection method

Pre-eclampsia/eclampsia is a serious disorder of human pregnancy that has a worldwide incidence of 2-10% and carries a severe morbidity and mortality risk for both mother and child. Its precise cause remains unknown. However, there is increasing evidence of an underlying complex maternal genetic susceptibility. Its high population incidence in the face of strong negative selection pressure suggests that the gene(s) involved have a selective advantage and/or a high mutation rate. One class of genetic diseases that involve a high mutation rate are the trinucleotide repeat expansion diseases. Thus, the aim of this study was to determine whether there is an association between a trinucleotide (CAG) repeat expansion and pre-eclampsia/eclampsia. We have used the repeat expansion detection (RED) method, which was developed to directly identify clinically significant repeat expansions, to analyse genomic DNA from an Australian and New Zealand population. The maximal CAG repeat length for each individual was recorded and the Mann-Whitney U and Wilcoxon rank sum test for independent samples were used to compare distributions for CAG/CTG repeats between two populations. There were no statistically significant differences between the distribution of CAG repeats in normotensive (n = 59) and severe pre-eclampsia (n = 69) (Mann-Whitney U = 1732; P = 0.14), and normotensive (n = 59) and eclamptic (n = 15) populations (Mann-Whitney U = 417, P = 0.726). Therefore, these RED results do not support a role for a large CAG expansion in pre-eclampsia/eclampsia. However, these data do not preclude the possibility that a small CAG expansion is associated with the disorder nor do they negate the hypothesis that a highly mutable gene contributes to the genetic component of pre-eclampsia/eclampsia.