The disorder involves attacks of muscle weakness or paralysis , alternating with periods of normal muscle function.
Attacks usually begin very early in life, often before the age of one year.
Attacks are usually frequent, but last for only 1 or 2 hours. They tend to occur while resting after exercise or exertion. In fact, there may be high or normal levels of potassium in the bloodstream both during and between attacks. Glucose and insulin administration, which trigger attacks of the other disorders, have no effect on hyperkalemic periodic paralysis. Administration of potassium, which is used to treat weakness associated with the other disorders, worsens the weakness.