Tada asked "Is the upper age limit of the study (80) simply for practical purposes (to many other things happening, memory lose and other system malfunctions)?"
I'm not sure. Probably practical purposes like you suggested. Based on 2015 data, 84% of patients with renal failure/end stage renal disease were under age 75. So there shouldn't be a problem recruiting patients....especially with only 44 being enrolled.
BearDownAZ