AVP and Down syndrome: Brain injury can cause alterations in Na+, K+, Ca2+, and other electrolyte levels, which can be used as a prognostic factor for mortality and morbidity following TBI [158,159,160]; for instance, an excessive release of antidiuretic hormone (ADH) may cause the syndrome of inappropriate antidiuretic hormone secretion (SIADH), leading to water retention and dilutional hyponatremia.