Clinical Characteristics

The encephalomyopathic crises include epilepsy, impaired gait, and altered mental status, and are often triggered by infection. Neurologic complications include progressive neurodegeneration, global developmental delay, intellectual disability, absent or dysarthric speech, epilepsy, hypotonia, ataxic or scissoring gait, weakness or spasticity in lower extremities, and dystonia in some. Cardiac features reported include intermittent long QTc interval, premature ventricular contraction, ventricular tachycardia, Torsade de pointes, ventricular fibrillation, cardiac arrest, and in some patients, hypertrophic cardiomyopathy.