The maternal X chromosome impairs cognition and accelerates brain aging through epigenetic modulation in female mice

Female mammalian cells harbor two X chromosomes, one of maternal and one of paternal origin. During development, one X randomly inactivates[1][1]–[4][2]. This renders either the maternal or paternal X active, causing X mosaicism that varies among individual females, with some showing considerable or complete skew in the general female population[5][3]–[7][4]. Parent-of-X-origin can modify epigenetics via DNA methylation[8][5], [9][6] and possibly gene expression; thus, mosaicism could buffer dysregulated processes in aging and disease. However, whether X skewing – or its mosaicism – alters functions in females is largely unknown. Here we tested whether skew toward the maternal X (Xm) influences key functions of the body. Among cardiac, bone, metabolic, and brain functions, Xm selectively impaired cognition in female mice throughout the lifespan. Cognitive deficits were accompanied by Xm-mediated acceleration of biologic or epigenetic aging of the female hippocampus, a key center for learning and memory. Xm showed epigenetic imprinting of several genes within hippocampal neurons, suggesting silenced cognitive loci. Thus, the maternal X chromosome impaired cognition, accelerated brain aging, and silenced genes. Understanding how the maternal X impairs brain function could lead to new understanding of female heterogeneity in cognitive heath and to X chromosome-derived pathways against cognitive deficits and brain aging. ### Competing Interest Statement The authors have declared no competing interest. [1]: #ref-1 [2]: #ref-4 [3]: #ref-5 [4]: #ref-7 [5]: #ref-8 [6]: #ref-9