LAUSR

Maternal microchimerism, the presence of a small number of maternal cells in the offspring, usually results from transfer of maternal cells during pregnancy, [1] or possibly during breastfeeding [2]. In 1999, the group of J. Lee Nelson demonstrated that microchimerism of maternal origin persists into adult life [3]. Maternal microchimerism seems to be evolutionary conserved, which suggests that maternal microchimerism has an evolutionary advantage and could be important for reproductive fitness and possibly disease [4]. In the current issue of EBiomedicine, Karlmark et al. present novel data indicating the presence of grandmaternal microchimerism in fetal cord blood [5]. This is the first time grandmaternal microchimerism has been presented as more than a theoretical possibility. The detection of grandmaternal genetic material in minute amounts calls for a meticulous methodological approach, the use of very specific and sensitive laboratory methods, and a study population consisting of multigenerational families. Working from an existing cohort of primigravid women and their offspring, Karlmark et al. detected DNA compatible with grandmaternal microchimerism in five of 28 cord blood samples, using HLA sequence-specific real time PCR. Karlmark et al. found grandmaternal microchimerism to be present in much lower quantities (»100 fold lower) and be less prevalent than maternal microchimerism in the same cohort (18% vs 57%, respectively) [5]. In this pioneering study, the number of study participants was limited, and only a few samples were positive for grandmaternal microchimerism. This is not surprising given the low quantities detected, and that three generations with specific HLA-genotype combinations are needed, which quickly winnows down the eligible participants from the study population. The low number of positive samples is also not surprising, as very low quantities of grandmaternal genetic material were reported. Theoretically, there could be other sources of the detected DNA. Undetected prior miscarriages,