G1D - Glucose transporter type 1 deficiency syndrome

a. What are movement disorders?

Movement disorders are a group of symptoms that indicate an impaired ability to produce and control body movement. Every body movement, from raising a hand to smiling, involves a complex interaction between the brain and spinal cord, nerves, and muscles. Damage to or malfunction of any of these components may result in a movement disorder. There is reason to believe that G1D movement disorders originate in the brain.

The term 'paroxysmal' is also often used, to indicate the abnormal movements are sudden and unpredictable, with a fairly rapid return to normal.

b. What movement disorders are seen in G1D?

• Ataxia is unsteady or poorly controlled movement due to problems with the control of coordination and balance.
• Dyskinesia, which simply means abnormal ('dys') movement ('kinesia'). Tics, spasm, athetosis (slow, writhing motions), chorea (rapid, randomly irregular jerky movements) and dystonia are all different types of dyskinesia.
• Chorea is repetitive, brief, jerky, rapid involuntary movements that start in one part of the body and move abruptly, unpredictably, and often continuously to another part.
• In dystonia there are sustained or persistent contractions of one or more muscles. This leads to abnormal postures or writhing, twisting movements of part of the body. There are many different types, with various muscles involved. Writer's cramp is an example of focal dystonia (limited to one group of muscles), causing bizarre postures in one arm when writing or typing and disappearing at rest.
• Myoclonus refers to quick, lightning-like jerks (contractions) of a muscle or a group of muscles. Myoclonus may involve only one hand, a group of muscles in the upper arm or leg, or a group of facial muscles. Or it may involve many muscles at the same time.

c. Can GDT cause movement disorders and also seizures?

Yes. Movement disorders may occur in G1D in isolation, in combination with other movement disorders, or in G1D patients who also have seizures and epilepsy.

d. How are G1D movement disorders treated?

The treatment of movement disorders in general may include several drugs prescribed by a neurologist. There is very limited experience with the use of these drugs in G1D, but there is no known reason to withhold any of these drugs in G1D, particularly if they show efficacy. However, the ketogenic diet has proven effective for the treatment of G1D-related movement disorders.