Isotopic H/D Exchange in Hydrogen Bonds Between the Nitrogenous Bases of the CAG Repeat Tract Makes It Possible to Stabilize Its Expansion in the ATXN2 Gene

<b>Background</b>: The isotopic composition of the body's internal environment can affect its functional state. Such effects are realized, among other things, by inserting deuterium atoms into hydrogen bonds between pairs of nitrogenous bases of DNA molecules and modifying their mechanical properties. <b>Methods</b>: This study uses a coarse-grained mathematical model of DNA. <b>Results</b>: It has been established that in a certain range of the magnitude of the torque, with the presence of a deuterium atom within it, stabilization of the CAG repeat tract is observed. In addition, it was found that, regardless of which base pair the deuterium atom falls into in the CAG repeat tract, its stability increases and the probability of hairpin formation decreases, which may interfere with the reading of genetic information from the site encoding glutamine. <b>Conclusions</b>: Single H/D substitutions in the CAG repeat tract of the <i>ATXN2</i> gene increase its stability by reducing the formation of open states, regardless of the position of deuterium.