Similarly in diabetes, individuals can't make enough insulin, so the cells are effectively " starving" even though they are surrounded by glucose in the blood.
In Prader-Willi, the hypothalamus has issues secreting gonadotropin releasing hormone and growth hormone releasing hormone as it should, which can cause decreased sex hormone levels and short stature, respectively.
People with type I diabetes don't make enough insulin, so when they eat a meal—especially a meal with a lot of potassium— that potassium sits in the blood instead of being taken into cells, and this causes hyperkalemia.