Hyperkalemia is really common and can be caused by lots of different things. I don't suppose you know what his potassium levels are? Mild hyperkalemia is usually asymptomatic, but severe hyperkalemia is very dangerous and can result in cardiac arrhythmias. Hyperkalemia is often indicative of kidney disfunction as potassium is usually excreted by the kidneys - if the kidneys are not functioning normally then the potassium is not excreted and high levels are found in the blood. The kidney disfunction can be the primary cause of the hyperkalemia, or the kidney disfunction may be secondary to another problem such as diabetes or adrenal issues.

There are so many unknowns. Stay away from google! I hope your friends DS is well soon.