Brain is often involved, with seizures, deafness, loss of balance and vision, and retardation common. Progression and severity vary. Muscle fatigue and weakness during and after exertion, with muscle soreness or cramping. Patients are often unable to attain previous performance levels yet condition is nondebilitating and nonprogressive. Low tolerance for exercise, with cramps often occuring after exercise.
Intense exercise can cause muscle destruction and possible damage to kidneys.
Reducing strenuous exercise can lessen severity. Muscle fatigue which upon exercise can lead to severe cramps, nausea, vomiting, muscle damage and discoloration of urine. Disease varies widely in severity and progression. Muscular pain, cramps, muscle damage and urine discoloration possible following intense exercise of brief duration. Severity varies and intense exercise should be avoided.