PTH and Huntington disease: Studies have also shown the association between parathyroid hormone (PTH) [5], plasma calcium (Ca) [5-6], and phosphorus (P) levels [6-7] with blood pressure (BP) in HD. While the P load has been reported to have an effect on endothelial dysfunction by increasing the production of reactive oxygen species and decreasing nitric oxide production via inhibitory phosphorylation of endothelial nitric oxide synthase [8].