REN and Huntington disease: Studies aimed at elucidating the pathophysiology of HTN HD patients concluded that 90% of cases resulted from sodium and volume overload (volume-dependent), while the majority of the remaining had elevated renin activity (renin-dependent), resulting in high blood pressure (BP) during HD.[5] The renin–angiotensin–aldosterone system (RAAS) is a signaling pathway responsible for regulating the body's BP.