The major features found in all the periodic paralyses are:
1. Attacks almost always begin before the age of 25, though occasionally later in life. ATS patients can develop first symptoms at any age.
2. Serum potassium fluctuates shortly before an attack, but serum potassium level will normalize before the attacks resolves and will be within the normal range between attacks. This is not a disorder of the blood but one in which there is an inappropriate shift of fluid, K+ and NA+ during attacks.