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Paroxysmal exertion-induced dyskinesia
Paroxysmal exertion-induced dyskinesia (PED) is a form of paroxysmal dyskinesia (see this term), characterized by painless attacks of dystonia of the extremities triggered by prolonged physical activities.
The prevalence is unknown but 20 sporadic cases and 9 families have been described to date.
The age of onset is usually in childhood, but may range from 1 to 30 years. PED is characterized by dyskinesias induced by prolonged exercise of 15-60 minutes of duration. The attacks last between 5 minutes and 2 hours and are typically restricted to the exercised limbs. The dystonic movements are usually bilateral and are aggravated by cold, psychological stress, fatigue and lack of sleep. The frequency of attacks varies between one per day to one per month. Brisk, deep tendon reflexes, developmental delay and intellectual disability (most frequently mild) may also be observed. In some familial forms, epilepsy or migraine can co-occur. PED can be associated with paroxysmal dystonic choreathetosis with episodic ataxia and spasticity, benign familial infantile seizures (BFIE), infantile convulsions and choreoathetosis (ICCA syndrome) or rolandic epilepsy - paroxysmal exercise-induced dystonia - writer's cramp (see these terms).
The pathophysiology of PED is still unknown but some familial cases were found to be associated with mutations in the SLC2A1 (solute carrier family 2 (facilitated glucose transporter), member 1) gene (1p34.2). SLC2A1 encodes the glucose transporter GLUT1. All mutations in this gene responsible for PED have been found to affect the ability of GLUT1 to transport glucose. It has thus been proposed that an energy deficiency upon exertion caused by a reduced glucose transport rate is a cause of this paroxysmal movement disorder in SLC2A1 related cases.
The diagnosis of PED relies on clinical examination and laboratory investigations showing hypoglycorrhachia and hypoglycemia. Electroencephalography (EEG) and brain imaging are normal. The diagnosis is confirmed by molecular genetic screening of SLC2A1 gene.
The differential diagnosis includes paroxysmal kinesigenic dyskinesia (PKD), young adult-onset Parkinsonism and encephalopathy due to GLUT1 deficiency (see these terms).
Prenatal diagnosis for pregnancies at increased risk of PED is possible by analysis of DNA extracted from fetal cells obtained by amniocentesis (usually performed at 15-18 weeks' gestation) or chorionic villus sampling (usually performed at 10-12 weeks' gestation). The disease-causing mutation of an affected family member must be identified in the family before prenatal testing can be performed.
Sporadic and familial cases with autosomal dominant mode of inheritance have been reported for PED. Genetic counseling should be offered to patients and families.
Management and treatment
There is no specific cure or treatment but avoiding precipitating events such as prolonged physical exercise may largely improve the symptoms. Moreover, a ketogenic diet for patients may prevent attacks and may lead to improvement of developmental delay in affected children.